Isolated cytochrome c oxidase deficiency in G93A SOD1 mice overexpressing CCS protein

G93A SOD1 transgenic mice overexpressing CCS protein develop an accelerated disease course that is associated with enhanced mitochondrial pathology and increased mitochondrial localization of mutant SOD1. Because these results suggest an effect of mutant SOD1 on mitochondrial function, we assessed the enzymatic activities of mitochondrial respiratory chain complexes in the spinal cords of CCS/G93A SOD1 and control mice. CCS/G93A SOD1 mouse spinal cord demonstrates a 55% loss of complex IV (cytochrome c oxidase) activity compared with spinal cord from age-matched non-transgenic or G93A SOD1 mice. In contrast, CCS/G93A SOD1 spinal cord shows no reduction in the activities of complex I, II, or III. Blue native gel analysis further demonstrates a marked reduction in the levels of complex IV but not of complex I, II, III, or V in spinal cords of CCS/G93A SOD1 mice compared with non-transgenic, G93A SOD1, or CCS/WT SOD1 controls. With SDS-PAGE analysis, spinal cords from CCS/G93A SOD1 mice showed significant decreases in the levels of two structural subunits of cytochrome c oxidase, COX1 and COX5b, relative to controls. In contrast, CCS/G93A SOD1 mouse spinal cord showed no reduction in levels of selected subunits from complexes I, II, III, or V. Heme A analyses of spinal cord further support the existence of cytochrome c oxidase deficiency in CCS/G93A SOD1 mice. Collectively, these results establish that CCS/G93A SOD1 mice manifest an isolated complex IV deficiency which may underlie a substantial part of mutant SOD1-induced mitochondrial cytopathy.     

Detergent-insoluble aggregates associated with amyotrophic lateral sclerosis in transgenic mice contain primarily full-length, unmodified superoxide dismutase-1

Determining the composition of aggregated superoxide dismutase 1 (SOD1) species associated with amyotrophic lateral sclerosis (ALS), especially with respect to co-aggregated proteins and post-translational modifications, could identify cellular or biochemical factors involved in the formation of these aggregates and explain their apparent neurotoxicity. The results of mass spectrometric and shotgun-proteomic analyses of SOD1-containing aggregates isolated from spinal cords of symptomatic transgenic ALS mice using two different isolation strategies are presented, including 1) resistance to detergent extraction and 2) size exclusion-coupled anti-SOD1 immunoaffinity chromatography. Forty-eight spinal cords from three different ALS-SOD1 mutant mice were analyzed, namely G93A, G37R, and the unnatural double mutant H46R/H48Q. The analysis consistently revealed that the most abundant proteins recovered from aggregate species were full-length unmodified SOD1 polypeptides. Although aggregates from some spinal cord samples contained trace levels of highly abundant proteins, such as vimentin and neurofilament-3, no proteins were consistently found to co-purify with mutant SOD1 in stoichiometric quantities. The results demonstrate that the principal protein in the high molecular mass aggregates whose appearance correlates with symptoms of the disease is the unmodified, full-length SOD1 polypeptide.     

A taxol-dependent procedure for the isolation of microtubules and microtubule-associated proteins (MAPs)

The effect of the antimitotic drug taxol on the association of MAPs (microtubule-associated proteins) with microtubules was investigated. Extensive microtubule assembly occurred in the presence of Taxol at 37 degrees C. at 0 degrees C, and at 37 degrees C in the presence of 0.35 M NaCl, overcoming the inhibition of assembly normally observed under the latter two conditions. At 37 degrees C and at 0 degrees C, complete assembly of both tubulin and the MAPs was observed in the presence of Taxol. However, at elevated ionic strength, only tubulin assembled, forming microtubules devoid of MAPs. The MAPs could also be released from the surface of preformed microtubules by exposure to elevated ionic strength. These properties provided the basis for a rapid new procedure for isolating microtubules and MAPs of high purity from small amounts of biological material. The MAPs could be recovered by exposure of the microtubules to elevated ionic strength and subjected to further analysis. Microtubules and MAPs were prepared from bovine cerebral cortex (gray matter) and from HeLa cells. MAP 1, MAP2, and the tau MAPs, as well as species of Mr = 28,000 and 30,000 (LMW, or low molecular weight, MAPs) and a species of Mr = 70,000 were isolated from gray matter. Species identified as the 210,000 and 125,000 mol wt HeLa MAPs were isolated from HeLa cells. Microtubules were also prepared for the first time from white matter. All of the MAPs identified in gray matter preparations were identified in white matter, but the amounts of individual MAP species differed. The most striking difference in the two preparations was a fivefold lower level of MAP 2 relative to tubulin in white matter than in gray. The high molecular weigh MAP, MAP1, was present in equal ratio to tubulin in white and gray matter. These results indicate that MAP 1 and MAP2, as well as other MAP species, may have a different cellular or subcellular distribution.     

Copper and zinc metallation status of copper-zinc superoxide dismutase from amyotrophic lateral sclerosis transgenic mice

Mutations in the metalloenzyme copper-zinc superoxide dismutase (SOD1) cause one form of familial amyotrophic lateral sclerosis (ALS), and metals are suspected to play a pivotal role in ALS pathology. To learn more about metals in ALS, we determined the metallation states of human wild-type or mutant (G37R, G93A, and H46R/H48Q) SOD1 proteins from SOD1-ALS transgenic mice spinal cords. SOD1 was gently extracted from spinal cord and separated into insoluble (aggregated) and soluble (supernatant) fractions, and then metallation states were determined by HPLC inductively coupled plasma MS. Insoluble SOD1-rich fractions were not enriched in copper and zinc. However, the soluble mutant and WT SOD1s were highly metallated except for the metal-binding-region mutant H46R/H48Q, which did not bind any copper. Due to the stability conferred by high metallation of G37R and G93A, it is unlikely that these soluble SOD1s are prone to aggregation in vivo, supporting the hypothesis that immature nascent SOD1 is the substrate for aggregation. We also investigated the effect of SOD1 overexpression and disease on metal homeostasis in spinal cord cross-sections of SOD1-ALS mice using synchrotron-based x-ray fluorescence microscopy. In each mouse genotype, except for the H46R/H48Q mouse, we found a redistribution of copper between gray and white matters correlated to areas of high SOD1. Interestingly, a disease-specific increase of zinc was observed in the white matter for all mutant SOD1 mice. Together these data provide a picture of copper and zinc in the cell as well as highlight the importance of these metals in understanding SOD1-ALS pathology.     

Selective stabilization of tau in axons and microtubule-associated protein 2C in cell bodies and dendrites contributes to polarized localization of cytoskeletal proteins in mature neurons

In mature neurons, tau is abundant in axons, whereas microtubule- associated protein 2 (MAP2) and MAP2C are specifically localized in dendrites. Known mechanisms involved in the compartmentalization of these cytoskeletal proteins include the differential localization of mRNA (MAP2 mRNA in dendrites, MAP2C mRNA in cell body, and Tau mRNA in proximal axon revealed by in situ hybridization) (Garner, C.C., R.P. Tucker, and A. Matus. 1988. Nature (Lond.). 336:674-677; Litman, P., J. Barg, L. Rindzooski, and I. Ginzburg. 1993. Neuron. 10:627-638), suppressed transit of MAP2 into axons (revealed by cDNA transfection into neurons) (Kanai, Y., and N. Hirokawa. 1995. Neuron. 14:421-432), and differential turnover of MAP2 in axons vs dendrites (Okabe, S., and N. Hirokawa. 1989. Proc. Natl. Acad. Sci. USA. 86:4127-4131). To investigate whether differential turnover of MAPs contributes to localization of other major MAPs in general, we microinjected biotinylated tau, MAP2C, or MAP2 into mature spinal cord neurons in culture (approximately 3 wk) and then analyzed their fates by antibiotin immunocytochemistry. Initially, each was detected in axons and dendrites, although tau persisted only in axons, whereas MAP2C and MAP2 were restricted to cell bodies and dendrites. Injected MAP2C and MAP2 bound to dendritic microtubules more firmly than to microtubules in axons, while injected tau bound to axonal microtubules more firmly than to microtubules in dendrites. Thus, beyond contributions from mRNA localization and selective axonal transport, compartmentalization of each of the three major MAPs occurs through local differential turnover.     

Characterization of microtubule-associated proteins in teleosts.

Although microtubules are known to play an important role in many cellular processes, they have been virtually neglected in fish. In this report, microtubule-associated proteins (MAPs) in fish (teleost) were characterized using antibodies (Abs) directed against the mammalian MAPs tau, MAP1A and B, and MAP 2. Two different populations of tau-like proteins (TLPs) were found in fish brain using the anti-tau Abs Tau-1, Tau-2, tau5', and tau3'. The TLPs that were recognized by Tau-1, Tau-2, and tau5' were (1) heat-stable; (2) the same molecular weight as mammalian TLPs: 59-62 kDa; (3) not enriched in microtubules prepared from catfish brain; and (4) localized to the cell body of neurons in fish brains. While the TLPs recognized by tau3' Abs were (1) heat-stable; (2) lower molecular weight than mammalian TLPs: 32-55 vs. 50-65 kDa; (3) enriched in microtubule fractions prepared from catfish brain, and (4) localized to the axons of neurons. These results are consistent with two different populations of TLPs being present in fish brains. While MAP2 was found to be approximately the same molecular weight, 250 kDa, in zebrafish and goldfish as in mammals and to be distributed to dendrites in the fish brain, both MAP1A and MAP1B were found to be about 25% the mass of their mammalian homologs. These results suggest that MAPS in fish have some characteristics similar to their mammalian counterparts, but also possess some unique properties that require further study to elucidate their function.     

Stable expression of heterologous microtubule-associated proteins (MAPs) in Chinese hamster ovary cells: evidence for differing roles of MAPs in microtubule organization

To study the effects of microtubule-associated proteins (MAPs) on in vivo microtubule assembly, cDNAs containing the complete coding sequences of a Drosophila 205-kD heat stable MAP, human MAP 4, and human tau were stably transfected into CHO cells. Constitutive expression of the transfected genes was low in most cases and had no obvious effects on the viability of the transfected cell lines. High levels of expression, as judged by Western blots, immunofluorescence, and Northern blots, could be induced by treating cells with sodium butyrate. High levels of MAPs were maintained for at least 24-48 h after removal of the sodium butyrate. Immunofluorescence analysis indicated that all three MAPs bound to cellular microtubules, but only the transfected tau caused a rearrangement of microtubules into bundles. Despite high levels of expression of these exogenous MAPs and the bundling of microtubules in cells expressing tau, transfected cells had normal levels of assembled and unassembled tubulin. With the exception of the tau-induced bundles, microtubules in transfected cells showed the same sensitivity as control cells to microtubule depolymerization by Colcemid. Further, all three MAPs were ineffective in reversing the taxol-dependent phenotype of a CHO mutant cell line. The absence of a quantitative effect of any of these heterologous proteins on the assembly of tubulin suggests that these MAPs may have different roles in vivo from those inferred previously from in vitro experiments.     

Overexpression of Abeta is associated with acceleration of onset of motor impairment and superoxide dismutase 1 aggregation in an amyotrophic lateral sclerosis mouse model

Transgenic mice carrying mutant Cu/Zn superoxide dismutase (SOD1) recapitulate the motor impairment of human amyotrophic lateral sclerosis (ALS). The amyloid-beta (Abeta) peptide associated with Alzheimer's disease is neurotoxic. To investigate the potential role of Abeta in ALS development, we generated a double transgenic mouse line that overexpresses SOD1(G93A) and amyloid precursor protein (APP)-C100. The transgenic mouse C100.SOD1(G93A) overexpresses Abeta and shows earlier onset of motor impairment but has the same lifespan as the single transgenic SOD1(G93A) mouse. To determine the mechanism associated with this early-onset phenotype, we measured copper and zinc levels in brain and spinal cord and found both significantly elevated in the single and double transgenic mice compared with their littermate control mice. Increased glial fibrillary acidic protein and decreased APP levels in the spinal cord of C100.SOD1(G93A) mice compared with the SOD1(G93A) mice agree with the neuronal damage observed by immunohistochemical analysis. In the spinal cords of C100.SOD1(G93A) double transgenic mice, soluble Abeta was elevated in mice at end-stage disease compared with the pre-symptomatic stage. Buffer-insoluble SOD1 aggregates were significantly elevated in the pre-symptomatic mice of C100.SOD1(G93A) compared with the age-matched SOD1(G93A) mice, correlating with the earlier onset of motor impairment in the C100.SOD1(G93A) mice. This study supports abnormal SOD1 protein aggregation as the pathogenic mechanism in ALS, and implicates a potential role for Abeta in the development of ALS by exacerbating SOD1(G93A) aggregation.     

Role of MAP1B in axonal retrograde transport of mitochondria

The MAPs (microtubule-associated proteins) MAP1B and tau are well known for binding to microtubules and stabilizing these structures. An additional role for MAPs has emerged recently where they appear to participate in the regulation of transport of cargos on the microtubules found in axons. In this role, tau has been associated with the regulation of anterograde axonal transport. We now report that MAP1B is associated with the regulation of retrograde axonal transport of mitochondria. This finding potentially provides precise control of axonal transport by MAPs at several levels: controlling the anterograde or retrograde direction of transport depending on the type of MAP involved, controlling the speed of transport and controlling the stability of the microtubule tracks upon which transport occurs.     

Insoluble mutant SOD1 is partly oligoubiquitinated in amyotrophic lateral sclerosis mice

Mutations in the Cu,Zn-superoxide dismutase (SOD1) gene cause a familial form of amyotrophic lateral sclerosis (ALS) through an unknown gain-of-function mechanism. Mutant SOD1 aggregation may be the toxic property. In fact, proteinaceous inclusions rich in mutant SOD1 have been found in tissues from the familial form of ALS patients and in mutant SOD1 animals, before disease onset. However, very little is known of the constituents and mechanism of formation of aggregates in ALS. We and others have shown that there is a progressive accumulation of detergent-insoluble mutant SOD1 in the spinal cord of G93A SOD1 mice. To investigate the mechanism of SOD1 aggregation, we characterized by proteome technologies SOD1 isoforms in a Triton X-100-insoluble fraction of spinal cord from G93A SOD1 mice at different stages of the disease. This showed that at symptomatic stages of the disease, part of the insoluble SOD1 is unambiguously mono- and oligoubiquitinated, in spinal cord and not in hippocampus, and that ubiquitin branches at Lys(48), the major signal for proteasome degradation. At presymptomatic stages of the disease, only insoluble unmodified SOD1 is recovered. Partial ubiquitination of SOD1-rich inclusions was also confirmed by immunohistochemical and electron microscopy analysis of lumbar spinal cord sections from symptomatic G93A SOD1 mice. On the basis of these results, we propose that ubiquitination occurs only after SOD1 aggregation and that oligoubiquitination may underline alternative mechanisms in disease pathogenesis.     

Microtubule-associated proteins and the determination of neuronal form

1. The assembly of microtubules is essential for the maintenance of both the extension and the radial symmetry of axons and dendrites. Microtubule-associated proteins (MAPs) are implicated in this function because they promote tubulin polymerization and because they appear to be involved in cross-linking microtubules in the neuritic cytoplasm. 2. In a variety of species high molecular weight MAP2 is found only in dendrites and MAP tau is found only is axons, indicating that certain MAPs are associated with specific aspects of neuronal morphology. 3. All neuronal MAPs that have been studied are under strong developmental regulation with either their form or abundance changing between developing and adult brain. In both rat and Xenopus the change from "early" to "late" MAP forms occurs concurrently with the cessation of axon and dendrite growth and the maturation of neuronal morphology. 4. In situations where neuronal growth persists in the adult, such as retinal photoreceptor cells and the olfactory system, "early" MAPs continue to be expressed in the adult brain. 5. These results implicate MAPs in neuronal morphogenesis and suggest that "early" MAPs are involved in axon and dendrite growth whereas the "late" MAPs are involved in the stabilization of their mature form.     

Selective loss of neurofilament expression in Cu/Zn superoxide dismutase (SOD1) linked amyotrophic lateral sclerosis

Neurofilament pathology is a hallmark of sporadic and familial amyotrophic lateral sclerosis (SALS and FALS). The disease mechanisms underlying this pathology are presently unclear, but recent evidence in SALS patients suggest that reductions in neurofilament light subunit (NFL) mRNA may contribute to the death of motor neurones. Mutations in the gene encoding Cu-Zn superoxide dismutase (SOD1) represent the best-studied cause of FALS, and a number of laboratory models of SOD1-mediated disease exist. Here we have used microdissected lumbar spinal cord motor neurones from human SOD1 FALS patients as well as G93A SOD1 transgenic mice and demonstrated that reduced NFL mRNA levels are seen in both. To probe the molecular mechanisms underpinning these observations, we generated NSC34 motor neurone-like cell lines expressing wild-type and mutant SOD1. NSC34 cells expressing G37R or G93A SOD1 showed selective reductions in NFL and NFM mRNA and protein. These data suggest that NFL mRNA reductions are common to SALS and FALS patients, and that cells and mice expressing mutant SOD1 may enable us to characterize the molecular mechanism(s) responsible for the loss of neurofilament mRNA.     

Redox proteomics analysis of oxidatively modified proteins in G93A-SOD1 transgenic mice--a model of familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron degenerative disease characterized by the loss of neuronal function in the motor cortex, brain stem, and spinal cord. Familial ALS cases, accounting for 10-15% of all ALS disease, are caused by a gain-of-function mutation in Cu,Zn-superoxide dismutase (SOD1). Two hypotheses have been proposed to explain the toxic gain of function of mutant SOD (mSOD). One is that mSOD can directly promote reactive oxygen species and reactive nitrogen species generation, whereas the other hypothesis suggests that mSODs are prone to aggregation due to instability or association with other proteins. However, the hypotheses of oxidative stress and protein aggregation are not mutually exclusive. G93A-SOD1 transgenic mice show significantly increased protein carbonyl levels in their spinal cord from 2 to 4 months and eventually develop ALS-like motor neuron disease and die within 5-6 months. Here, we used a parallel proteomics approach to investigate the effect of the G93A-SOD1 mutation on protein oxidation in the spinal cord of G93A-SOD1 transgenic mice. Four proteins in the spinal cord of G93A-SOD1 transgenic mice have higher specific carbonyl levels compared to those of non-transgenic mice. These proteins are SOD1, translationally controlled tumor protein (TCTP), ubiquitin carboxyl-terminal hydrolase-L1 (UCH-L1), and, possibly, alphaB-crystallin. Because oxidative modification can lead to structural alteration and activity decline, our current study suggests that oxidative modification of UCH-L1, TCTP, SOD1, and possibly alphaB-crystallin may play an important role in the neurodegeneration of ALS.     

Calpain-mediated proteolysis of microtubule associated proteins MAP1B and MAP2 in developing brain

Microtubule associated proteins MAP1B and MAP2 are important components of the neuronal cytoskeleton. During early development of the brain, MAP1B (340 kDa) is present as two isoforms that differ in their level of phosphorylation, while MAP2 is expressed as a single high molecular weight isoform (MAP2B, 280 kDa) and a low molecular weight form (MAP2C, 70 kDa). In this study we examined and compared the sensitivities of MAP1B and MAP2, obtained from MT preparations and brain homogenates of young rats, to degradation by calcium-activated neutral protease, calpain II. We found that in MAPs prepared from microtubules the two isoforms of MAP1B had comparable sensitivity to calpain-mediated proteolysis. Similarly, the high and low molecular weight forms of MAP2 were equally sensitive to digestion by calpain. However, although both MAPs were very susceptible to calpain-mediated proteolysis, MAP1B was more resistant to degradation by calpain than MAP2. Furthermore, the endogenous degradation of MAPs in neonate brain homogenates was calcium-dependent and inhibited by leupeptin, and the pattern of degradation products for MAP1B and MAP2 was similar to that of calpain-mediated proteolysis. These data suggest that calpain can play a role in the regulation of MAPs levels during brain development, in relation to normal neuronal differentiation and disorders associated with neurodegeneration.     

Protein Oxidative Damage in a Transgenic Mouse Model of Familial Amyotrophic Lateral Sclerosis

Abstract: The Gly⁹³→Ala mutation in the Cu,Zn superoxide dismutase (Cu,Zn-SOD) gene (SOD1) found in some familial amyotrophic lateral sclerosis (FALS) patients has been shown to result in an aberrant increase in hydroxyl radical production by the mutant enzyme that may cause oxidative injury to spinal motor neurons. In the present study, we analyzed the extent of oxidative injury to lumbar and cervical spinal cord proteins in transgenic FALS mice that overexpress the SOD1 mutation [TgN(SOD1-G93A)G1H] in comparison with nontransgenic mice. Total protein oxidation was examined by spectrophotometric measurement of tissue protein carbonyl content by the dinitrophenylhydrazine (DNPH) assay. Four ages were investigated: 30 (pre-motor neuron pathology and clinical disease), 60 (after initiation of pathology, but pre-disease), 100 (～50% loss of motor neurons and function), and 120 (near complete hindlimb paralysis) days. Protein carbonyl content in 30-day-old TgN(SOD1-G93A)G1H mice was twice as high as the level found in age-matched nontransgenic mice. However, at 60 and 100 days of age, the levels were the same. Then, between 100 and 120 days of age, the levels in the TgN(SOD1-G93A)G1H mice increased dramatically (557%) compared with either the nontransgenic mice or transgenic animals that overexpress the wild-type human Cu,Zn-SOD [TgN(SOD1)N29]. The 100–120-day increase in spinal cord protein carbonyl levels was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoretic separation and western blot immunoassay, which enabled the identification of heavily oxidized individual proteins using a monoclonal antibody against DNPH-derivatized proteins. One of the more heavily oxidized protein bands (14 kDa) was identified by immunoprecipitation as largely Cu,Zn-SOD. Western blot comparison of the extent of Cu,Zn-SOD protein carbonylation revealed that the level in spinal cord samples from 120-day-old TgN(SOD1-G93A)G1H mice was significantly higher than that found in age-matched nontransgenic or TgN(SOD1)N29 mice. These results suggest that the increased hydroxyl radical production associated with the G93A SOD1 mutation and/or lipid peroxidation-derived radical species (peroxyl or alkoxyl) causes extensive protein oxidative injury and that the Cu,Zn-SOD itself is a key target, which may compromise its antioxidant function.     

Exendin-4 ameliorates motor neuron degeneration in cellular and animal models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by a progressive loss of lower motor neurons in the spinal cord. The incretin hormone, glucagon-like peptide-1 (GLP-1), facilitates insulin signaling, and the long acting GLP-1 receptor agonist exendin-4 (Ex-4) is currently used as an anti-diabetic drug. GLP-1 receptors are widely expressed in the brain and spinal cord, and our prior studies have shown that Ex-4 is neuroprotective in several neurodegenerative disease rodent models, including stroke, Parkinson's disease and Alzheimer's disease. Here we hypothesized that Ex-4 may provide neuroprotective activity in ALS, and hence characterized Ex-4 actions in both cell culture (NSC-19 neuroblastoma cells) and in vivo (SOD1 G93A mutant mice) models of ALS. Ex-4 proved to be neurotrophic in NSC-19 cells, elevating choline acetyltransferase (ChAT) activity, as well as neuroprotective, protecting cells from hydrogen peroxide-induced oxidative stress and staurosporine-induced apoptosis. Additionally, in both wild-type SOD1 and mutant SOD1 (G37R) stably transfected NSC-19 cell lines, Ex-4 protected against trophic factor withdrawal-induced toxicity. To assess in vivo translation, SOD1 mutant mice were administered vehicle or Ex-4 at 6-weeks of age onwards to end-stage disease via subcutaneous osmotic pump to provide steady-state infusion. ALS mice treated with Ex-4 showed improved glucose tolerance and normalization of behavior, as assessed by running wheel, compared to control ALS mice. Furthermore, Ex-4 treatment attenuated neuronal cell death in the lumbar spinal cord; immunohistochemical analysis demonstrated the rescue of neuronal markers, such as ChAT, associated with motor neurons. Together, our results suggest that GLP-1 receptor agonists warrant further evaluation to assess whether their neuroprotective potential is of therapeutic relevance in ALS.     

Hydrogen-deuterium exchange in vivo to measure turnover of an ALS-associated mutant SOD1 protein in spinal cord of mice

Mutations of cytosolic Cu/Zn superoxide dismutase 1 (SOD1) in humans and overexpression of mutant human SOD1 genes in transgenic mice are associated with the motor neuron degenerative condition known as amyotrophic lateral sclerosis (ALS; Lou Gehrig's disease). Gain-of-function toxicity from the mutant protein expressed in motor neurons, associated with its misfolding and aggregation, leads to dysfunction and cell death, associated with paralyzing disease. Here, using hydrogen-deuterium exchange in intact mice in vivo, we have addressed whether an ALS-associated mutant protein, G85R SOD1-YFP, is subject to the same rate of turnover in spinal cord both early in the course of the disease and later. We find that the mutant protein turns over about 10-fold faster than a similarly expressed wild-type fusion and that there is no significant change in the rate of turnover as animals age and disease progresses.     

Stabilization of hyperdynamic microtubules is neuroprotective in amyotrophic lateral sclerosis

Mutations in copper/zinc superoxide dismutase 1 (SOD1), a genetic cause of human amyotrophic lateral sclerosis, trigger motoneuron death through unknown toxic mechanisms. We report that transgenic SOD1G93A mice exhibit striking and progressive changes in neuronal microtubule dynamics from an early age, associated with impaired axonal transport. Pharmacologic administration of a microtubule-modulating agent alone or in combination with a neuroprotective drug to symptomatic SOD1G93A mice reduced microtubule turnover, preserved spinal cord neurons, normalized axonal transport kinetics, and delayed the onset of symptoms, while prolonging life by up to 26%. The degree of reduction of microtubule turnover was highly predictive of clinical responses to different treatments. These data are consistent with the hypothesis that hyperdynamic microtubules impair axonal transport and accelerate motor neuron degeneration in amyotrophic lateral sclerosis. Measurement of microtubule dynamics in vivo provides a sensitive biomarker of disease activity and therapeutic response and represents a new pharmacologic target in neurodegenerative disorders.     

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

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

Early abnormalities in transgenic mouse models of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative and fatal human disorder characterized by progressive loss of motor neurons. Transgenic mouse models of ALS are very useful to study the initial mechanisms underlying this neurodegenerative disease. We will focus here on the earlier abnormalities observed in superoxide dismutase 1 (SOD1) mutant mice. Several hypotheses have been advanced to explain the selective loss of motor neurons such as apoptosis, neurofilament disorganisation, oxidative stress, mitochondrial dysfunction, astrogliosis and excitotoxicity. Although disease onset appears at adulthood, recent studies have detected abnormalities during embryonic and postnatal maturation in animal models of ALS. We reported that SOD1(G85R) mutant mice exhibit specific delays in acquiring sensory-motor skills during the first week after birth. In addition, physiological measurements on in vitro spinal cord preparations reveal defects in evoking rhythmic activity with N-methyl-DL-aspartate and serotonin at lumbar, but not sacral roots. This is potentially significant, as functions involving sacral roots are spared at late stages of the disease. Moreover, electrical properties of SOD1 lumbar motoneurons are altered as early as the second postnatal week when mice begin to walk. Alterations concern the input resistance and the gain of SOD1 motoneurons which are lower than in control motoneurons. Whether or not the early changes in discharge firing are responsible for the uncoupling between motor axon terminals and muscles is still an open question. A link between these early electrical abnormalities and the late degeneration of motoneurons is proposed in this short review. Our data suggest that ALS, as other neurodegenerative diseases, could be a consequence of an abnormal development of neurons and network properties. We hypothesize that the SOD1 mutation could induce early changes during the period of maturation of motor systems and that compensatory mechanisms-linked to developmental spinal plasticity-might explain the late onset of the disease.