Transgenic mice carrying a human mutant superoxide dismutase transgene develop neuronal cytoskeletal pathology resembling human amyotrophic lateral sclerosis lesions

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

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

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

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

Early onset of severe familial amyotrophic lateral sclerosis with a SOD-1 mutation: potential impact of CNTF as a candidate modifier gene

Mutations in the copper/zinc superoxide dismutase 1 (SOD-1) gene are found in approximately 20% of patients with familial amyotrophic lateral sclerosis (FALS), or amyotrophic lateral sclerosis 1. Here we describe a 25-year-old male patient who died from FALS after a rapid disease course of 11 mo. Sequencing of the SOD-1 gene revealed a heterozygous T-->G exchange at position 1513 within exon 5, coding for a V-->G substitution at position 148 of the mature protein. Genetic analysis of this family revealed the same mutation in both his healthy 35-year-old sister and his mother, who did not develop the disease before age 54 years. Screening for candidate modifier genes that might be responsible for the early onset and severe course of the disease in the 25-year-old patient revealed an additional homozygous mutation of the CNTF gene not found in his yet unaffected sister. hSOD-1G93A mice were crossbred with CNTF(-/-) mice and were investigated with respect to disease onset and duration, to test the hypothesis that CNTF acts as a candidate modifier gene in FALS with mutations in the SOD-1 gene. Such hSOD-1G93A/CNTF-deficient mice develop motoneuron disease at a significantly earlier stage than hSOD-1G93A/CNTF-wild-type mice. Linkage analysis revealed that the SOD-1 gene was solely responsible for the disease. However, disease onset as a quantitative trait was regulated by the allelic constitution at the CNTF locus. In addition, patients with sporadic amyotrophic lateral sclerosis who had a homozygous CNTF gene defect showed significantly earlier disease onset but did not show a significant difference in disease duration. Thus, we conclude that CNTF acts as a modifier gene that leads to early onset of disease in patients with FALS who have SOD-1 mutations, in patients with sporadic amyotrophic lateral sclerosis, and in the hSOD-1G93A mouse model.

Overexpression of neurofilament H disrupts normal cell structure and function

Studying exogenously expressed tagged proteins in live cells has become a standard technique for evaluating protein distribution and function. Typically, expression levels of experimentally introduced proteins are not regulated, and high levels are often preferred to facilitate detection. However, overexpression of many proteins leads to mislocalization and pathologies. Therefore, for normative studies, moderate levels of expression may be more suitable. To understand better the dynamics of intermediate filament formation, transport, and stability in a healthy, living cell, we inserted neurofilament heavy chain (NFH)-green fluorescent protein (GFP) fusion constructs in adenoviral vectors with tetracycline (tet)-regulated promoters. This system allows for turning on or off the synthesis of NFH-GFP at a selected time, for a defined period, in a dose-dependent manner. We used this inducible system for live cell imaging of changes in filament structure and cell shape, motility, and transport associated with increasing NFH-GFP expression. Cells with low to intermediate levels of NFH-GFP were structurally and functionally similar to neighboring, nonexpressing cells. In contrast, overexpression led to pathological alterations in both filament organization and cell function.

Emerging strategies for drug development in motor neuron disease

Until recently, attempts to identify disease-modifying treatments in motor neuron disease have largely failed. This was due to a lack of understanding of the disease pathogenesis and poor clinical trial design. Recent advances in the genetics of motor neuron disease and the maturation of tissue culture techniques have increased our understanding of the mechanisms of cell death in motor neuron disease. This has in turn led to better in vitro and transgenic animal models, allowing for a more systematic study of the disease process and analysis of potential therapeutic agents. With the advent of these models, motor neuron disease drug research has entered a new era. It is now possible to pursue mass screening of compounds in the in vitro models. Successful compounds in vitro can be advanced to the transgenic animal models. Once toxicity and potential therapeutic effects in animals are known, agents which remain promising can be taken to Phase I, II and III clinical trials. This will increase the likelihood of success and is more desirable than methods previously utilised. A hierarchical approach such as this will be even more important as multi-drug regimens are to be studied. The number of combinations for these multi-drug regimens becomes prohibitive without a screening method.

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

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

Leukemia inhibitory factor by systemic administration rescues spinal motor neurons in the SOD1 G93A murine model of familial amyotrophic lateral sclerosis

Leukemia inhibitory factor (LIF) is a survival factor for motoneurons. In this study we investigated whether intense systemic LIF therapy prevents the loss of lumbar motoneurons in the transgenic SOD1 G93A mouse model of familial amyotrophic lateral sclerosis. Treatment involved daily 25 microg/kg intraperitoneal injection for a period of 6 weeks starting at 70 days of age. Using the unbiased optical dissector technique, significant rescue of motoneurons in the LIF-treated group (3809+/-455) was found compared to the vehicle group (1085+/-140).

Stabilization of mutant Cu/Zn superoxide dismutase (SOD1) protein by coexpressed wild SOD1 protein accelerates the disease progression in familial amyotrophic lateral sclerosis mice

Transgenic mice carrying familial amyotrophic lateral sclerosis (FALS)-linked mutant Cu/Zn superoxide dismutase (SOD1) genes such as G93A (G93A-mice) and G85R (G85R-mice) genes develop limb paresis. Introduction of human wild type SOD1 (hWT-SOD1) gene, which does not cause motor impairment by itself, into different FALS mice resulted in different effects on their clinical courses, from no effect in G85R-mice to acceleration of disease progression in G93A-mice. However, the molecular mechanism which causes the observed difference, has not been clarified. We hypothesized that the difference might be caused by the stability of mutant SOD1 proteins. Using a combination of mass spectrometry and enzyme-linked immunosorbent assay, we found that the concentration of G93A-SOD1 protein was markedly elevated in tissues of transgenic mice carrying both G93A- and hWT-SOD1 genes (G93A/hWT-mice) compared to that in G93A-mice, and also found that the concentration of G93A-SOD1 protein had a close relation to the disease duration. The concentration of metallothionein-I/II in the spinal cord, reflecting the degree of copper-mediated oxidative stress, was highest in G93A/hWT-mice, second in G93A-mice, and normal in the mice carrying hWT-SOD1 gene. These results indicated that the increase of G93A-SOD1 protein was responsible for the increase of oxidative stress and disease acceleration in G93A/hWT-mice. We speculate that coexpression of hWT-SOD1 protein is deleterious to transgenic mice carrying a stable mutant such as G93A-SOD1, because this mutant protein is stabilized by hWT-SOD1 protein, but not to transgenic mice carrying an unstable mutant such as G85R-SOD1, because this mutant protein is not stabilized by hWT-SOD1.

Reactive oxygen species and mitochondrial diseases

A variety of diseases have been associated with excessive reactive oxygen species (ROS), which are produced mostly in the mitochondria as byproducts of normal cell respiration. The interrelationship between ROS and mitochondria suggests shared pathogenic mechanisms in mitochondrial and ROS-related diseases. Defects in oxidative phosphorylation can increase ROS production, whereas ROS-mediated damage to biomolecules can have direct effects on the components of the electron transport system. Here, we review the molecular mechanisms of ROS production and damage, as well as the existing evidence of mitochondrial ROS involvement in human diseases.

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

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

Cellular changes in motoneurons in a transgenic mouse model for amyotrophic lateral sclerosis as revealed by monoclonal antibody Py

Transgenic mice (G93A) carrying the human amyotrophic lateral sclerosis (ALS) linked superoxide dismutase 1 (SOD1) mutations develop a motoneuron disease resembling human ALS. The affected motoneurons are characterized by the presence of cellular alterations. The antigen recognized by the monoclonal antibody Py is suggested to be associated with the neurofilamentous and microtubular elements of the cytoskeleton of specific neuron populations including the spinal motoneurons. The aim of the present study was to measure changes in the relative Py-immunoreactivity per identified Choline-Acetyl-Transferase (ChAT)-immunoreactive motoneuron during the disease progression. The relative Py-immunoreactivity of identified spinal motoneurons was measured on double stained (Py and ChAT) motoneurons using a digital imaging system coupled to an inverse microscope. A significant decrease of Py-immunoreactivity was already noted in the pre-symptomatic stages of the disease even before the onset of massive motoneuron degeneration. It is concluded that the Py-antibody detects early intracellular abnormalities related to neurodegenerative changes in spinal motoneurons of transgenic SOD1-(G93A) mice.

Progress in clinical neurosciences: the evidence for ALS as a multisystems disorder of limited phenotypic expression

Traditionally, amyotrophic lateral sclerosis (ALS) is considered to be a unique neurodegeneration disorder in which motor neurons are selectively vulnerable to a single disease process. Our current understanding of ALS, however, suggests that this is far too limited an approach. While motor neuron degeneration remains the central component to this process, there is considerable phenotypic variability including broad ranges in survivorship and the presence or absence of cognitive impairment. The number of familial variants of ALS for which unique genetic linkage has been identified is increasing, attesting further to the biological heterogeneity of the disorder. At the cellular level, derangements in cytoskeletal protein and glutamate metabolism, mitochondrial function, and in glial interactions are clearly evident. When considered in this fashion, ALS can be justifiably considered a disorder of multiple biological processes sharing in common the degeneration of motor neurons.

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

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

Cytokine upregulation in a murine model of familial amyotrophic lateral sclerosis

Although pronounced changes in astrocytes and microglia accompany the neuronal degeneration observed in a murine model of familial amyotrophic lateral sclerosis, the significance of non-neuronal cell contribution to the disease process remains unclear. Activated astrocytes and microglia are capable of secreting numerous cytokines, some of which may have potentially harmful effects on neuron survival. For this reason we wished to determine the expression pattern of various cytokines in the spinal cords of transgenic mice expressing a Cu-Zn superoxide dismutase mutation (Tgn G93A SOD1) by using semi-quantitative RT-PCR. Three different patterns of cytokine expression were observed in G93A SOD1 transgenic mice. For most cytokines, we were unable to detect mRNA expression in Tgn G93A SOD1 mouse spinal cords at any age, yet message was readily detected in spleen or activated splenocytes. A second pattern, typified by TNF-alpha, was characterized by mRNA expression prior to the onset of motor deficits and increasing until the terminal stages of the disease. For other cytokines, including TGF-beta1 and M-CSF, mRNA expression was detected in young presymptomatic Tgn G93A SOD1 mice (as well as wild-type and transgenic mice expressing wild-type SOD1 (Tgn SOD1)), with upregulation later occurring only in G93A SOD1 transgenic mice. These results indicate a temporal correlation between the expression of certain cytokines and the onset of motor dysfunction in Tgn G93A SOD1 mice and suggest a potential role for these molecules in the disease.

Induction of proinflammatory molecules in mice with amyotrophic lateral sclerosis: no requirement for proapoptotic interleukin-1beta in neurodegeneration

Recent studies have demonstrated the activation of caspase-1 and caspase-3 in mice expressing mutant superoxide dismutase 1 (SOD1), models of amyotrophic lateral sclerosis. Caspase-1 converts the prointerleukin-1beta into a potent proinflammatory molecule involved in the innate immune response and in neurodegenerative diseases. We report on the chronic expression of interleukin-1beta mRNA in the spinal cord of SOD1G37R mice, together with robust mRNA expression for the nuclear factor-kappaB (NF-kappaB) inhibitor IkappaBalpha, for other proinflammatory cytokines and chemokines (interleukin-6, tumor necrosis factor-alpha, monocyte chemoattractant protein-1) and for the toll-like receptor TLR2 involved in innate immunity. To further assess the interleukin-1beta contribution to neurodegeneration, we generated mice expressing SOD1G37R in a context of interleukin-1beta gene knockout. Surprisingly, the absence of interleukin-1beta had no effect on the life span of SOD1G37R mice, nor on the extent of motor axon degeneration at age 7 and 10 months. Whereas neither compensatory induction of the interleukin-1alpha mRNA nor increases in mRNA levels for IkappaBalpha, tumor necrosis factor-alpha and macrophage chemoattractant protein-1 occurred as a result of interleukin-1beta gene disruption, enhanced levels of TLR2 mRNA were detected in SOD1G37R mice lacking interleukin-1beta. We conclude that interleukin-1beta does not directly contribute to motor neuron degeneration in SOD1G37R mice, but it may act as a modulator of the innate immune response.

Apoptotic death of neurons exhibiting peripherin aggregates is mediated by the proinflammatory cytokine tumor necrosis factor-alpha

Peripherin, a neuronal intermediate filament protein associated with axonal spheroids in amyotrophic lateral sclerosis (ALS), induces the selective degeneration of motor neurons when overexpressed in transgenic mice. To further clarify the selectivity and mechanism of peripherin-induced neuronal death, we analyzed the effects of peripherin overexpression in primary neuronal cultures. Peripherin overexpression led to the formation of cytoplasmic protein aggregates and caused the death not only of motor neurons, but also of dorsal root ganglion (DRG) neurons that were cultured from dissociated spinal cords of peripherin transgenic embryos. Apoptosis of DRG neurons containing peripherin aggregates was dependent on the proinflammatory central nervous system environment of spinal cultures, rich in activated microglia, and required TNF-alpha. This synergistic proapoptotic effect may contribute to neuronal selectivity in ALS.

Genetically engineered models relevant to neurodegenerative disorders: their value for understanding disease mechanisms and designing/testing experimental therapeutics

Significant progress in the identification of disease-specific genes for a variety of neurodegenerative diseases have provided opportunities to understand molecular mechanisms and to test experimental therapeutic for these disorders. Recent works on clarifying the selective vulnerability of neurons and pathogenic mechanisms using genetically engineered mouse models of familial forms of Alzheimer's disease and motor neuron disease will be reviewed.

Ubiquitin immunoreactivity in presumed spinal interneurones in motor neurone disease

Previous studies have demonstrated the presence of ubiquitin-immunoreactivity (Ub-IR) as inclusions and skeins in motor neurones of both the familial and sporadic forms of motor neurone disease (MND). There is evidence that interneurones also degenerate in MND, but Ub-IR in ventral horn spinal interneurones has not been studied previously. Here, Ub-IR was investigated in 1445 presumed interneurones and 1086 presumed motor neurones counted in three random 20-microm sections of the ventral horn of the third lumbar segment of the spinal cord of each of seven controls and seven patients with MND. The ventral horn was divided into four quadrants; the dorsomedial quadrant contains almost exclusively interneurones and the ventrolateral quadrant largely motor neurones. The neurones were also classified by morphological and size criteria into presumed interneurones (< 25 microm) and presumed motor neurones (>or= 25 microm). Ub-IR was classified as inclusions, skeins and dispersed cytoplasmic and nuclear staining. Ub-IR inclusions or skeins were not observed in the controls but 6.6% of neurones (motor neurones and interneurones) showed the presence of dispersed cytoplasm staining and nuclear staining. The incidence of Ub-IR cytoplasmic and nuclear staining was significantly greater in both motor neurones and interneurones of MND patients than controls. Ub-IR was less frequent in MND cases in which a great loss of neurones was observed. Ub-IR was significantly more frequent in motor neurones than interneurones, both in patients and controls. Ub-IR inclusions and skeins were only observed in motor neurones from MND patients. Ub-IR inclusions were not observed in presumed spinal interneurones, while skeins were only seen in three out of 565 of these cells (two of them in the dorsomedial quadrant) in two out of seven patients. Thus, although presumed spinal interneurones occasionally revealed Ub-IR features similar to motor neurones, the rare staining of Ub-IR skeins and the lack of Ub-IR inclusions in interneurones in MND suggests that these neurones only occasionally form ubiquitin-protein conjugates. Neuronal size, rather than type, may be important in determining whether ubiquitin-protein conjugates form in the ventral horn neurones in MND.

Synaptic sprouting increases the uptake capacities of motoneurons in amyotrophic lateral sclerosis mice

Using adenoviruses encoding reporter genes as retrograde tracers, we assessed the capacity of motoneurons to take up and retrogradely transport adenoviral particles injected into the muscles of transgenic mice expressing the G93A human superoxide dismutase mutation, a model of amyotrophic lateral sclerosis. Surprisingly, transgene expression in the motoneurons was significantly higher in symptomatic mice than in control or presymptomatic mice. Using botulinum toxin to induce nerve sprouting at neuromuscular junctions, we showed that the unexpectedly high level of motoneurons retrograde transduction results, at least in part, from newly acquired uptake properties of the sprouts. These findings demonstrate the remarkable uptake properties of amyotrophic lateral sclerosis motoneurons in response to denervation and the rationale of using intramuscular injections of adenoviruses to overexpress therapeutic proteins in motor neuron diseases.

Galectin-1 is a component of neurofilamentous lesions in sporadic and familial amyotrophic lateral sclerosis

In amyotrophic lateral sclerosis (ALS), abnormal accumulation of neurofilaments induces pathological changes such as axonal spheroids, cord-like neurite swellings, and perikaryal conglomerate inclusions in degenerating motor neurons of the spinal cord, and the accumulation seems to cause motor neuron degeneration in this disease. Such ALS lesions were intensely labeled with HepSS-1, a monoclonal antibody to heparan sulfate. Since the identification of HepSS-1-immunoreactive substance seems to be an important step for understanding the molecular pathology of ALS, we purified the substance from human spinal cord tissue to homogeneity. Amino acid sequence of the protein was consistent with that of galectin-1. Immunohistochemistry using antibodies against recombinant human galectin-1 showed that galectin-1 was accumulated in these lesions in ALS. Although HepSS-1 was believed to be specific for heparan sulfate, it reacted with recombinant human galectin-1 which has no heparan sulfate moiety. The results show that galectin-1 is a component of the neurofilamentous lesions in ALS. Since galectin-1 has axonal regeneration-enhancing activity, the abnormal accumulation of galectin-1 to the lesions seems to be related to the pathological process of ALS.

Induction of polysialic acid-neural cell adhesion molecule in surviving motoneurons of transgenic amyotrophic lateral sclerosis mice

The highly polysialylated neural cell adhesion molecule (PSA-NCAM) is recognized as a marker of neurogenesis or neural plasticity in adult nervous system. PSA-NCAM expression was examined in the spinal cord of transgenic mice harboring a mutant Cu/Zn superoxide dismutase (SOD1) gene. Immunohistochemistry showed a progressive expression of PSA-NCAM in surviving motoneurons of spinal ventral horns from an early and presymptomatic stage (25 weeks) before significant loss of ventral horn neurons, while no detectable PSA-NCAM in the ventral horn of non-transgenic littermates during the ageing process. The present data suggest that a specific expression of PSA-NCAM may be involved in the survival of spinal motoneurons under pathological conditions such as amyotrophic lateral sclerosis.

Age-dependent induction of congophilic neurofibrillary tau inclusions in tau transgenic mice

Intraneuronal filamentous tau inclusions such as neurofibrillary tangles (NFTs) are neuropathological hallmarks of Alzheimer's disease (AD) and related sporadic and familial tauopathies. NFTs identical to those found in AD brains have also been detected in the hippocampus and entorhinal cortex of cognitively normal individuals as they age. To recapitulate age-induced NFT formation in a mouse model, we examined 12- to 24-month-old transgenic (Tg) mice overexpressing the smallest human brain tau isoform. These Tg mice develop congophilic tau inclusions in several brain regions including the hippocampus, amygdala, and entorhinal cortex. NFT-like inclusions were first detected in Tg mice at 18 to 20 months of age and they were detected by histochemical dyes that bind specifically to crossed beta-pleated sheet structures (eg, Congo red, Thioflavin S). Moreover, ultrastructurally these lesions contained straight tau filaments comprised of both mouse and human tau proteins but not other cytoskeletal proteins (eg, neurofilaments, microtubules). Isolated tau filaments were also recovered from detergent-insoluble tau fractions and insoluble tau proteins accumulated in brain in an age-dependent manner. Thus, overexpression of the smallest human brain tau isoform resulted in late onset and age-dependent formation of congophilic tau inclusions with properties similar to those in the tangles of human tauopathies, thereby implicating aging in the pathogenesis of fibrous tau inclusions.

Human Cu/Zn superoxide dismutase (SOD1) overexpression in mice causes mitochondrial vacuolization, axonal degeneration, and premature motoneuron death and accelerates motoneuron disease in mice expressing a familial amyotrophic lateral sclerosis mutant SOD1

Cytosolic Cu/Zn superoxide dismutase (SOD1) is a ubiquitous small cytosolic metalloenzyme that catalyzes the conversion of superoxide anion to hydrogen peroxide (H(2)O(2)). Mutations in the SOD1 gene cause a familial form of amyotrophic lateral sclerosis (fALS). The mechanism by which mutant SOD1s causes ALS is not understood. Transgenic mice expressing multiple copies of fALS-mutant SOD1s develop an ALS-like motoneuron disease resembling ALS. Here we report that transgenic mice expressing a high concentration of wild-type human SOD1 (hSOD1(WT)) develop an array of neurodegenerative changes consisting of (1) swelling and vacuolization of mitochondria, predominantly in axons in the spinal cord, brain stem, and subiculum; (2) axonal degeneration in a number of long fiber tracts, predominantly the spinocerebellar tracts; and (3) at 2 years of age, a moderate loss of spinal motoneurons. Parallel to the development of neurodegenerative changes, hSOD1(WT) mice also develop mild motor abnormalities. Interestingly, mitochondrial vacuolization was associated with accumulation of hSOD1 immunoreactivity, suggesting that the development of mitochondrial pathology is associated with disturbed SOD1 turnover. In this study we also crossed hSOD1(WT) mice with a line of fALS-mutant SOD1 mice (hSOD1(G93A)) to generate "double" transgenic mice that express high levels of both wild-type and G93A mutant hSOD1. The "double" transgenic mice show accelerated motoneuron death, earlier onset of paresis, and earlier death as compared with hSOD1(G93A) littermates. Thus in vivo expression of high levels of wild-type hSOD1 is not only harmful to neurons in itself, but also increases or facilitates the deleterious action of a fALS-mutant SOD1. Our data indicate that it is important for motoneurons to control the SOD1 concentration throughout their processes, and that events that lead to improper synthesis, transport, or breakdown of SOD1 causing its accumulation are potentially dangerous.

Gene therapy for amyotrophic lateral sclerosis and other motor neuron diseases

There are several incurable diseases of motor neuron degeneration, including amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, hereditary spastic hemiplegia, spinal muscular atrophy, and bulbospinal atrophy. Advances in gene transfer techniques coupled with new insights into molecular pathology have opened promising avenues for gene therapy aimed at halting disease progression. Nonviral preparations and recombinant adenoviruses, adeno-associated viruses, herpesviruses, and lentiviruses may ultimately transduce sufficient numbers of cerebral, brainstem, and spinal cord neurons for therapeutic applications. This could be accomplished by direct injection, transduction of lower motor neurons via retrograde transport after intramuscular injection, or cell-based therapies. Studies using transgenic mice expressing mutant superoxide dismutase 1 (SOD1), a model for one form of ALS, established that several proteins were neuroprotective, including calbindin, bcl-2, and growth factors. These same molecules promoted neuronal survival in other injury models, suggesting general applicability to all forms of ALS. Potentially correctable genetic lesions have also been identified for hereditary spastic hemiplegia, bulbospinal atrophy, and spinal muscular atrophy. Finally, it may be possible to repopulate lost corticospinal and lower motor neurons by transplanting stem cells or stimulating native progenitor populations. The challenge ahead is to translate these basic science breakthroughs into workable clinical practice.

Formation of high molecular weight complexes of mutant Cu, Zn-superoxide dismutase in a mouse model for familial amyotrophic lateral sclerosis

Deposition of aggregated protein into neurofilament-rich cytoplasmic inclusion bodies is a common cytopathological feature of neurodegenerative disease. How-or indeed whether-protein aggregation and inclusion body formation cause neurotoxicity are presently unknown. Here, we show that the capacity of superoxide dismutase (SOD) to aggregate into biochemically distinct, high molecular weight, insoluble protein complexes (IPCs) is a gain of function associated with mutations linked to autosomal dominant familial amyotrophic lateral sclerosis. SOD IPCs are detectable in spinal cord extracts from transgenic mice expressing mutant SOD several months before inclusion bodies and motor neuron pathology are apparent. Sequestration of mutant SOD into cytoplasmic inclusion bodies resembling aggresomes requires retrograde transport on microtubules. These data indicate that aggregation and inclusion body formation are mechanistically and temporally distinct processes.

Cytoskeletal abnormalities in amyotrophic lateral sclerosis: beneficial or detrimental effects?

Cytoskeletal abnormalities have been reported in cases of amyotrophic lateral sclerosis (ALS) including abnormal inclusions containing neurofilaments (NFs) and/or peripherin, reduced mRNA levels for the NF light (NF-L) protein and mutations in the NF heavy (NF-H) gene. Recently, transgenic mouse approaches have been used to address whether cytoskeletal changes may contribute to motor neuron disease. Mice lacking one of the three NF subunits are viable and do not develop motor neuron disease. Nonetheless, mice with null mutations for NF-L or for both NF-M and NF-H genes developed severe atrophy of ventral and dorsal root axons. The atrophic process is associated with hind limb paralysis during aging in mice deficient for both NF-M and NF-H proteins. The overexpression in mice of transgenes coding for wild-type or mutant NF proteins can provoke abnormal NF accumulations, axonal atrophy and sometimes motor dysfunction. However, the perikaryal NF accumulations are generally well tolerated by motor neurons and, except for expression of a mutant NF-L transgene, they did not provoke massive motor neuron death. Increasing the levels of perikaryal NF proteins may even confer protection in motor neuron disease caused by ALS-linked mutations in the superoxide dismutase (SOD1). In contrast, the overexpression of wild-type peripherin, a type of IF gene upregulated by inflammatory cytokines, provoked the formation of toxic IF inclusions with the high-molecular-weight NF proteins resulting in the death of motor neurons during aging. These results together with the detection of peripherin inclusions at early stage of disease in mice expressing mutant SOD1 suggest that IF inclusions containing peripherin may play a contributory role in ALS pathogenesis.

Reduction of axonal caliber does not alleviate motor neuron disease caused by mutant superoxide dismutase 1

It is well established that motor neurons with large axon caliber are selectively affected in amyotrophic lateral sclerosis (ALS). To investigate whether high neurofilament (NF) content and large axonal caliber are factors that predispose motor neurons to selective degeneration in ALS, we generated mice expressing a mutant form of superoxide dismutase 1 (SOD1(G37R)) linked to familial ALS in a context of one allele for each NF gene being disrupted. A approximately 40% decrease of NF protein content detected in triple heterozygous knockout mice shifted the calibers of large axons in L5 ventral root from 5-9 microm to 1-5 microm, altering neither the normal subunit stoichiometry and morphological distribution of NFs nor levels of other cytoskeletal proteins. This considerable reduction in NF burden and caliber of axons did not extend the life span of SOD1(G37R) mice nor did it alleviate the loss of motor axons. Moreover, increasing the density of NFs in axons by overexpressing a NF-L transgene did not accelerate disease in SOD1(G37R) mice. These results do not support the current view that high NF content and large caliber of axons may account for the selective vulnerability of motor neurons in ALS caused by mutant SOD1.

Early and selective pathology of light chain neurofilament in the spinal cord and sciatic nerve of G86R mutant superoxide dismutase transgenic mice

Pathologic accumulation of neurofilament protein (NF), both within spheroids of the proximal axon and within inclusions of motor neuron somata, is a hallmark of neurodegeneration in amyotrophic lateral sclerosis (ALS). Transgenic mice that express mutations in superoxide dismutase (SOD-1), which were genetically linked to familial ALS, develop symptomatology and pathology that strongly resemble ALS and therefore provide a useful model for studying the disease. Examining NF in the G86R mutant SOD-1 transgenic mice, we previously demonstrated that phosphorylated NF accumulates in motor neuron somata of symptomatic transgenic mice. In the present study, we expand these results by examining the immunocytochemical distribution of the three subunits of NF (i.e., light, medium, and heavy chains) as well as tubulin in presymptomatic and symptomatic SOD-1 transgenic mice. Although all NF subunits, but not tubulin, accumulate along with phosphorylated NF in the spinal cord inclusions of symptomatic mice, numerous inclusions containing only light chain NF are found in the spinal cord of presymptomatic SOD-1 transgenic mice. In addition to these results in the spinal cord, intensely immunoreactive aggregates of NF-L, but not the other NF subunits or tubulin, were observed in the sciatic nerve of both symptomatic and presymptomatic mutant SOD-1 transgenic mice. These results suggest that the mechanism of NF alteration in SOD-1 transgenic mice, and also perhaps in ALS patients, originates with the disruption of NF-L, only later involving the other subunits.

Neurofilament-rich intraneuronal inclusions exacerbate neurodegenerative sequelae of brain trauma in NFH/LacZ transgenic mice

Several neurodegenerative disorders are characterized by filamentous inclusions in neurons that selectively degenerate. The role these inclusions play in neuron degeneration is unclear, but this issue can be investigated experimentally in relevant animal models. The NFH/LacZ transgenic (TG) mice overexpress the high-molecular-weight neurofilament (NF) subunit (NFH) fused to beta-galactosidase, and these hybrid proteins aggregate into NF-rich, filamentous neuronal cytoplasmic inclusions (NCIs) that have been implicated in the progressive, age-dependent degeneration in subsets of affected neurons. Thus, these TG mice recapitulate some of the key pathology of neurodegenerative disorders with intraneuronal inclusions. To determine if the NCIs compromise neuron survival following traumatic brain injury (TBI), 3- to 6-month old TG and wild-type (WT) mice were subjected to TBI or sham injury. At 2 weeks post-TBI, the TG group showed increased TUNEL staining and activated caspase-3 immunoreactivity in cells of cerebral cortex, adjacent white matter, and hippocampus underlying the injury site, relative to control mice, but this labeling decreased at 4 weeks and was minimal thereafter. Compared to control mice, by 8 weeks postinjury, the TG mice showed a marked decrease in neuron density and increased gliosis in the hippocampal dentate gyrus and CA3 region as well as in the lateral thalamus, while the few remaining CA3 neurons exhibited cytoskeletal alterations, decreased synaptic protein immunoreactivity, and dissolution of NCIs. The more profound long-term neurodegenerative sequelae of TBI in the NFH/LacZ mice compared to WT mice suggest that the presence of intraneuronal inclusions may impair the recovery and long-term viability of injured neurons.

Formation of intermediate filament protein aggregates with disparate effects in two transgenic mouse models lacking the neurofilament light subunit

Protein aggregates containing intermediate filaments (IFs) are a hallmark of degenerating spinal motor neurons in amyotrophic lateral sclerosis (ALS). Recently, we reported that a deficiency in neurofilament light subunit (NF-L), a phenomenon associated with ALS, promoted the formation of IF inclusions with ensuing motor neuron death in transgenic mice overproducing peripherin, a type III IF protein detected in axonal inclusions of ALS patients. To further assess the role of NF-L in the formation of abnormal IF inclusions, we generated transgenic mice overexpressing human neurofilament heavy subunits (hNF-H) in a context of targeted disruption of the NF-L gene (hH;L-/- mice). The hH;L-/- mice exhibited motor dysfunction, and they developed nonfilamentous protein aggregates containing NF-H and peripherin proteins in the perikarya of spinal motor neurons. However, the perikaryal protein aggregates in the hH;L-/- mice did not provoke motor neuron death, unlike toxic IF inclusions induced by peripherin overexpression in NF-L null mice (Per;L-/- mice). Our results indicate that different types of IF protein aggregates with distinct properties may occur in a context of NF-L deficiency and that an axonal localization of such aggregates may be an important factor of toxicity.

Formation of intermediate filament protein aggregates with disparate effects in two transgenic mouse models lacking the neurofilament light subunit

Protein aggregates containing intermediate filaments (IFs) are a hallmark of degenerating spinal motor neurons in amyotrophic lateral sclerosis (ALS). Recently, we reported that a deficiency in neurofilament light subunit (NF-L), a phenomenon associated with ALS, promoted the formation of IF inclusions with ensuing motor neuron death in transgenic mice overproducing peripherin, a type III IF protein detected in axonal inclusions of ALS patients. To further assess the role of NF-L in the formation of abnormal IF inclusions, we generated transgenic mice overexpressing human neurofilament heavy subunits (hNF-H) in a context of targeted disruption of the NF-L gene (hH;L-/- mice). The hH;L-/- mice exhibited motor dysfunction, and they developed nonfilamentous protein aggregates containing NF-H and peripherin proteins in the perikarya of spinal motor neurons. However, the perikaryal protein aggregates in the hH;L-/- mice did not provoke motor neuron death, unlike toxic IF inclusions induced by peripherin overexpression in NF-L null mice (Per;L-/- mice). Our results indicate that different types of IF protein aggregates with distinct properties may occur in a context of NF-L deficiency and that an axonal localization of such aggregates may be an important factor of toxicity.

Calcium dynamics and buffering in oculomotor neurones from mouse that are particularly resistant during amyotrophic lateral sclerosis (ALS)-related motoneurone disease

Motoneurones are particularly vulnerable both in human forms of amyotrophic lateral sclerosis (ALS) and corresponding animal models of the disease. While most motoneurone populations are selectively impaired, oculomotor neurones are essentially resistant to ALS-related damage. Motoneurone vulnerability has been closely linked to disruptions of calcium signalling. To investigate underlying events, we performed a quantitative analysis of calcium homeostasis in oculomotor neurones from mice by simultaneous patch-clamp recordings in sliced tissue and microfluorometric-calcium measurements. Somatic calcium dynamics were investigated by using a computer-controlled microfluorometric system. In oculomotor neurones, basal calcium concentrations were around 80 nM and depolarisation-induced calcium responses were observed for membrane voltages positive to -40 u1u1u approximately mV1 approximately . Endogenous calcium homeostasis was quantified by using the 'added buffer' approach. The recovery phase of depolarisation-induced calcium transients was well approximated by a mono-exponential function with a decay time constant that showed a linear dependence on dye concentration. The extrapolated time constant in the absence of indicator dye was 1.7 +/- 0.2 s (n = 11 cells, 21C). Endogenous calcium binding ratios (kappa(s)) were found to be 264 +/- 25 (n = 11 cells), indicating that 99.6 % of cytosolic calcium ions were taken up by endogenous buffers. Recovery of calcium transients was characterised by an 'effective' extrusion rate gamma = 156 +/- 20 s-1 (n = 11 cells, 21 C). Endogenous calcium binding ratios in oculomotor neurones were 5- to 6-fold larger compared with those of more vulnerable motoneurones in the nucleus hypoglossus and spinal cord. In a first order approximation, they reduced the volume of local calcium elevations around open calcium channels, lowered peak amplitudes of global calcium transients for a given influx and prolonged calcium recovery times for a given set of uptake and extrusion mechanisms. With respect to motoneurone degeneration, our measurements suggest that the exceptional stability of oculomotor neurones partially results from a specialised calcium homeostasis based on high buffering capacities. Furthermore, they indicate that cellular adaptations that account for rapid calcium signalling in hypoglossal and spinal motoneurones enhance their vulnerability during ALS-related motoneurone disease.

The prostate apoptosis response-4 protein participates in motor neuron degeneration in amyotrophic lateral sclerosis

Prostate apoptosis response-4 (Par-4), a protein containing a leucine zipper domain within a death domain, is up-regulated in prostate cancer cells and hippocampal neurons induced to undergo apoptosis. Here, we report higher Par-4 levels in lumbar spinal cord samples from patients with amyotrophic lateral sclerosis (ALS) than in lumbar spinal cord samples from neurologically normal patients. We also compared the levels of Par-4 in lumbar spinal cord samples from wild-type and transgenic mice expressing the human Cu/Zn-superoxide dismutase gene with a familial ALS mutation. Relative to control samples, higher Par-4 levels were observed in lumbar spinal cord samples prepared from the transgenic mice at a time when they had hind-limb paralysis. Immunohistochemical analyses of human and mouse lumbar spinal cord sections revealed that Par-4 is localized to motor neurons in the ventral horn region. In culture studies, exposure of primary mouse spinal cord motor neurons or NSC-19 motor neuron cells to oxidative insults resulted in a rapid and large increase in Par-4 levels that preceded apoptosis. Pretreatment of the motor neuron cells with a Par-4 antisense oligonucleotide prevented oxidative stress-induced apoptosis and reversed oxidative stress-induced mitochondrial dysfunction that preceded apoptosis. Collectively, these data suggest a role for Par-4 in models of motor neuron injury relevant to ALS.

Metallothionein expression is altered in a transgenic murine model of familial amyotrophic lateral sclerosis

Missense mutations in the gene encoding copper zinc superoxide dismutase (SOD1) have been found to cause one form of familial amyotrophic lateral sclerosis (FALS). Although the exact mechanism of disease is unknown, abnormalities in the ability of mutant SOD1 to bind zinc or copper ions may be crucial in the pathogenesis of disease. Because members of the metallothionein (MT) family of zinc and copper binding proteins function as important cellular regulators of metal ion bioavailability in the central nervous system, we used in situ hybridization and immunohistochemistry to study the expression pattern of these molecules in a transgenic mouse model of familial ALS. In adult wild-type mouse spinal cord, expression of MT-I and MT-II is restricted to ependymal cells and a subset of astrocytes located in white matter tracts, while MT-III synthesis is limited to neurons within gray matter. Compared to wild-type littermates, transgenic mice carrying the G93A SOD1 mutation demonstrate markedly increased expression of MT-I and MT-II within astrocytes in both white and gray matter as weakness develops. MT-III synthesis in neurons is also greatly upregulated as G93A SOD1 animals age, with glial cell expression of MT-III evident by later stages of the disease. Changes in MT expression occur before the onset of motor deficits or significant motor neuron pathology in G93A SOD1 mice and remarkably extend beyond ventral horn populations of neurons and glia. These results are consistent with the hypothesis that metallothioneins may serve an early and important protective function in FALS.

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

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

What transgenic mice tell us about neurodegenerative disease

The recent broad advance in our understanding of human neurodegenerative diseases is based on the application of a new molecular approach. Through linkage analysis, the genes responsible for Huntington's disease, the spinocerebellar ataxias, and familial forms of Alzheimer's disease and amyotrophic lateral sclerosis (ALS) have been identified and cloned. The characterization of pathogenic mutations in such genes allows the creation of informative transgenic mouse models as, without exception, the genetic forms of adult neurodegenerative disease are due to toxicity of the mutant protein. Transgenic models provide insight into the oxidative mechanisms in ALS pathogenesis, the pathogenicity of expanded polyglutamine tracts in CAG triplet repeat disorders, and amyloidogenesis in Alzheimer's disease. Although such models have their limitations, they currently provide the best entry point for the study of human neurodegenerative diseases.

Restricted expression of G86R Cu/Zn superoxide dismutase in astrocytes results in astrocytosis but does not cause motoneuron degeneration

Evidence garnered from both human autopsy studies and genetic animal models has suggested a potential role for astrocytes in the pathogenesis of amyotrophic lateral sclerosis (ALS). Currently, mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) represent the only known cause of motoneuron loss in the disease, producing 21q linked familial ALS (FALS). To determine whether astrocytic dysfunction has a primary role in familial ALS, we have generated multiple lines of transgenic mice expressing G86R mutant SOD1 restricted to astrocytes. In GFAP-m SOD1 mice, astrocytes exhibit significant hypertrophy and increased GFAP reactivity as the animals mature. However, GFAP-mutant SOD1 transgenic mice develop normally and do not experience spontaneous motor deficits with increasing age. Histological examination of spinal cord in aged GFAP-mSOD1 mice reveals normal motoneuron and microglial morphology. These results indicate that 21q linked FALS is not a primary disorder of astrocytes, and that expression of mutant SOD1 restricted to astrocytes is not sufficient to cause motoneuron degeneration in vivo. Expression of mutant SOD1 in other cell types, most likely neurons, is critical for the initiation of disease.

The neuronal Golgi apparatus is fragmented in transgenic mice expressing a mutant human SOD1, but not in mice expressing the human NF-H gene

Fragmentation of the Golgi apparatus (GA) of motor neurons was first described in sporadic amyotrophic lateral sclerosis (ALS) and later confirmed in transgenic mice expressing the G93A mutation of the gene encoding the enzyme Cu,Zn superoxide dismutase (SOD1(G93A)) found in some cases of familial ALS. In these transgenic mice, however, the fragmentation of the neuronal GA was associated with cytoplasmic and mitochondrial vacuoles not seen in ALS. The present new series of transgenic mice expressing 14-17 trans gene copies of SOD1(G93A), compared to 25 copies in the mice we studied previously, showed consistent fragmentation of the GA of spinal cord motor neurons, axonal swellings, Lewy-like body inclusions in neurons and glia, but none of the cytoplasmic or mitochondrial vacuoles originally reported. Thus, this animal model recapitulates the clinical and most neuropathological findings of sporadic ALS. Neurofilaments (NF) accumulate in axons and, less often, in neuronal perikarya in most cases of sporadic ALS and they have been implicated in its pathogenesis. In order to investigate whether fragmentation of the neuronal GA also occurs in association with accumulation of perikaryal NFs, we studied the organelle in transgenic mice expressing the heavy subunit of human neurofilaments (NF-H) which developed a motor neuronopathy resembling ALS. The neuronal GA of mice expressing NF-H, however, was intact despite massive accumulation of NFs in both perikarya and axons of motor neurons. In contrast, in transgenic mice expressing SOD1(G93A), the GA was fragmented despite the absence of accumulation of perikaryal NFs. These findings suggest that, in transgenic mice with neuronopathies caused by the expression of mutant SOD1(G93A) or the human NF-H, the GA and the perikaryal NFs are independently involved in the pathogenesis. The evidence suggests that the GA plays a central role in the pathogenesis of the vast majority of sporadic ALS and in FALS with SOD1 mutations.

Restricted expression of G86R Cu/Zn superoxide dismutase in astrocytes results in astrocytosis but does not cause motoneuron degeneration

Evidence garnered from both human autopsy studies and genetic animal models has suggested a potential role for astrocytes in the pathogenesis of amyotrophic lateral sclerosis (ALS). Currently, mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1) represent the only known cause of motoneuron loss in the disease, producing 21q linked familial ALS (FALS). To determine whether astrocytic dysfunction has a primary role in familial ALS, we have generated multiple lines of transgenic mice expressing G86R mutant SOD1 restricted to astrocytes. In GFAP-m SOD1 mice, astrocytes exhibit significant hypertrophy and increased GFAP reactivity as the animals mature. However, GFAP-mutant SOD1 transgenic mice develop normally and do not experience spontaneous motor deficits with increasing age. Histological examination of spinal cord in aged GFAP-mSOD1 mice reveals normal motoneuron and microglial morphology. These results indicate that 21q linked FALS is not a primary disorder of astrocytes, and that expression of mutant SOD1 restricted to astrocytes is not sufficient to cause motoneuron degeneration in vivo. Expression of mutant SOD1 in other cell types, most likely neurons, is critical for the initiation of disease.

Differential vulnerability of oculomotor, facial, and hypoglossal nuclei in G86R superoxide dismutase transgenic mice

In recent years, several mouse models of amyotrophic lateral sclerosis (ALS) have been developed. One, caused by a G86R mutation in the superoxide dismutase-1 (SOD-1) gene associated with familial ALS, has been subjected to extensive quantitative analyses in the spinal cord. However, the human form of ALS includes pathology elsewhere in the nervous system. In the present study, analyses were extended to three motor nuclei in the brainstem. Mutant mice and control littermates were evaluated daily, and mutants, along with their littermate controls, were killed when they were severely affected. Brains were removed after perfusion and processed for Nissl staining, the samples were randomized, and the investigators were blinded to their genetic status. Stereologic methods were used to estimate the number of neurons, mean neuronal volumes, and nuclear volume in three brainstem motor nuclei known to be differentially involved in the human form of the disease, the oculomotor, facial, and hypoglossal nuclei. In the facial nucleus, neuron number consistently declined (48%), an effect that was correlated with disease severity. The nuclear volume of the facial nucleus was smaller in the SOD-1 mutant mice (45.7% difference from control mice) and correlated significantly with neuron number. The oculomotor and hypoglossal nuclei showed less extreme involvement (<10% neuronal loss overall), with a trend toward fewer neurons in the hypoglossal nucleus of animals with severe facial nucleus involvement. In the oculomotor nucleus, neuronal loss was seen only once in five mice, associated with very severe disease. There was no significant change in the volume of individual neurons in any of these three nuclei in any transgenic mouse. These results suggest that different brainstem motor nuclei are differentially affected in this SOD-1 mutant model of ALS. The relatively moderate and late involvement of the hypoglossal nucleus indicates that, although the general patterns of neuronal pathology match closely those seen in ALS patients, some differences exist in this transgenic model compared with the progression of the disease in humans. However, these patterns of cellular vulnerability may provide clues for understanding the differential susceptibility of neural structures in ALS and other neurodegenerative diseases.

A mouse model of familial amyotrophic lateral sclerosis expressing a mutant superoxide dismutase 1 shows evidence of disordered transport in the vasopressin hypothalamo-neurohypophysial axis

Amyotrophic lateral sclerosis (ALS) is a fatal, paralytic disorder that primarily affects motoneurons. By combining physiological and morphological approaches, we examined the effect of a murine superoxide dismutase 1 (SOD1) mutation (G86R), which induces neurological disorders resembling human familial ALS (FALS), on the arginine vasopressin (AVP) hypothalamo-neurohypophysial axis, an unmyelinated tract poor in neurofilaments. First, we observed that G86R mice progressively consumed more water than wild-type littermates. Furthermore, levels of plasma AVP and neurohypophysial AVP content were decreased in the SOD1 mutant mice, whereas the amount of hypothalamic AVP increased in an age-dependent manner. However, hypothalamic AVP mRNA levels were not significantly modified in these animals. At the ultrastructural level, we found that the neurohypophysis of G86R mice had a decreased number of neurosecretory axons. Conversely, the presence of large axon swellings was more pronounced in the SOD1 mutant mice. In addition, the size of neurosecretory granules was higher in G86R than in wild-type animals. All these findings strongly suggest that the FALS-associated SOD1 mutation injures the hypothalamo-neurohypophysial axis by provoking early, progressive disturbances in the axonal transport of neurosecretory products from neuronal perikarya to nerve terminals. This blockade could ultimately result in degeneration of the tract, as proposed for the myelinated, neurofilament-enriched motor axons affected by ALS.

Transcriptional induction of metallothionein-I and -II genes in the livers of Cu,Zn-superoxide dismutase knockout mice

The levels of metallothionein-I and -II (MT-I and MT-II) mRNAs were elevated (10- to 12-fold), specifically in the livers of mice with homozygous deletion of the gene for Cu,Zn-SOD (Sod1-/-), the enzyme that catalyzes the removal of O(-)(2). The induction of MT mRNA occurred primarily at the level of transcription. In vivo genomic footprinting of the MT-I promoter region revealed distinctive footprinting at MRE-d, MRE-c, and MLTF/ARE sites in the livers of knockout mice. MTF-1, the key factor responsible for the heavy-metal and oxidative stress-induced expression of the MT-I gene, was activated 3-fold in the nuclear extract from the livers of Cu,Zn-SOD null mice. Because metallothioneins are potent scavengers of reactive oxygen species and protect cells from oxidative stress, the apparent normal characteristics of the mice with the disrupted Cu, Zn-SOD gene are probably due to overexpression of MT-I and MT-II in the livers of these animals.

Expression of MHC class I heavy chain and beta2-microglobulin in rat brainstem motoneurons and nigral dopaminergic neurons

We demonstrate here that motoneurons and nigral dopaminergic neurons in the brainstem of the adult rat, with the exception of motoneurons innervating ocular muscles, display high levels of both MHC class I heavy chain and beta2-microglobulin mRNAs. These neurons also display interferon-gamma receptor mRNA. We find it striking that these particular neurons are those which are vulnerable to neurodegeneration in diseases such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS).

Motor neurone metabolism

The cell and molecular mechanisms which determine the motor neurone (MN) phenotype are unclear. Tissue culture models offer a unique system for the study of a wide variety of MN features. For instance, since the neurone-astrocyte metabolic interactions play a critical role in the selective MN loss observed in amyotrophic lateral sclerosis (ALS), the glutamatergic MN toxicity could be reanalyzed in vitro, after a careful evaluation of the role of astrocytes. Ca(2+) appears to be important in inducing MN loss from in vitro studies. It was shown primarily in culture that apoptotic or necrotic death of neurones after injury depends upon the cell energetic status. Also, SOD-1 mutations were successfully expressed in cultured MNs, providing a critical assay to sequence the molecular processes responsible for MN degeneration due to an identified genetic defect. Purified human developing MNs and astrocytes were recently obtained from the spinal cord anterior horn. The effects of molecules affecting MN survival, neurite extension, and metabolism can easily be tested in long-term cultures. Interactions at the single cell level can be studied today using a series of RNA amplification techniques. Understanding the properties of human MNs in vitro may represent a critical tool in defining regional metabolic changes that could constitute the first pathogenic event of cell degeneration in ALS.

Neurofilament metabolism in sporadic amyotrophic lateral sclerosis

Although the role of intraneuronal neurofilamentous aggregates in the pathogenesis of ALS is unknown, their presence forms a key neuropathological hallmark of the disease process. Conversely, the experimental induction of neurofilamentous aggregates in either neurotoxic or transgenic mice gives rise to motor system degeneration. To determine whether alterations in the physiochemical properties of NF are present in sporadic ALS, we purified NF subunit proteins from cervical spinal cord of ALS and age-matched control patients. The cytoskeleton-enriched, Triton X-100 insoluble fraction was further separated into individual NF subunits using hydroxyapatite HPLC. We observed no differences between control and ALS in the characteristics of NFH, including migration patterns on 2D-IEF, sensitivity to E. coli, alkaline phosphatase mediated dephosphorylation, peptide mapping, or proteolysis (calpain, calpain/calmodulin mediated, phosphorylated or dephosphorylated NFH). NFL showed no differences in 2D-IEF migration patterns, peptide mapping, or the extent of NFL nitrotyrosine immunoreactivity in either the Triton soluble or insoluble fractions. The latter observation demonstrated that NFL nitration is a ubiquitous occurrence in neurons and suggests that NFL might function as a sink for free reactive nitrating species. In contrast to the lack of differences in the post-translational processing of NF in ALS, we did observe a selective suppression of NFL steady state mRNA levels in the limb innervating lateral motor neuron column of ALS. This occurred in the absence of modifications in NFH, NFM or neuronal nitric oxide synthase (Type I NOS; nNOS) steady state mRNA levels. Coupled with previous observations of nNOS immunoreactivity co-localizing with NF aggregates in ALS motor neurons, this suggests activation of the nNOS enzyme complex in ALS, which would be predicted to contribute directly to the generation of reactive nitrating species. Given this, the isolated suppression of NFL steady state mRNA levels in ALS may indicate that ALS motor neurons are at an intrinsic deficit in the ability to buffer free reactive nitrating species.

Experimental models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disease characterized by the progressive loss of motor neurons, leading to profound weakness and eventual death of affected individuals. For the vast majority of patients with ALS, the etiology of the disorder is unknown, and although multiple clinical trials of various therapeutic agents have been undertaken, truly effective therapy is not currently available for the disease. The selection of treatments used in ALS clinical trials frequently has its basis in promising data obtained from experimental model systems in which the proposed agent has shown some effect in protecting motor neurons from a particular insult. The likelihood of a successful clinical outcome for a given treatment in ALS would therefore depend on two principal factors, including the similarity of the model to the disease and the biologic action of the potential therapeutic agent. Partly because early experimental models of ALS failed to replicate the disease process, treatment success in these models did not carry over into human trials. Recently, however, a variety of newer model systems have been developed and utilized to investigate motor neuron degeneration as related to ALS. For example, in this issue, Corse et al. use a rat spinal cord organotypic slice subjected to glutamate excitotoxicity as a model system to test the effectiveness of neurotrophic factors in preventing motor neuron degeneration. This review will assess the strengths and weaknesses of differing ALS model systems that have been used to preclinically test potential drug efficacy in ALS.

Bcl-2 overexpression does not protect neurons from mutant neurofilament-mediated motor neuron degeneration

Transgenic mice with a point mutation in the light neurofilament gene develop amyotrophic lateral sclerosis-like motor neuron disease characterized by selective spinal motor neuron loss, neurofilamentous accumulations, and severe muscle atrophy. To test whether the large motor neurons at risk in this disease could be protected from mutant neurofilament-mediated killing, these mice were bred to mice overexpressing the human Bcl-2 proto-oncogene. Elevated levels of Bcl-2 increased the numbers of motor and sensory axons surviving after the developmental period of naturally occurring cell death but did not greatly reduce the number of degenerating axons or protect the large motor neurons from mutant neurofilament-mediated death.