Time course of neuropathology in the spinal cord of G86R superoxide dismutase transgenic mice

The Ile35 Residue of the ALS-Associated Mutant SOD1 Plays a Crucial Role in the Intracellular Aggregation of the Molecule

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with an unknown pathogenesis. It has been reported that mutations in the gene for Cu/Zn superoxide dismutase (SOD1) cause familial ALS. Mutant SOD1 undergoes aggregation and forms amyloid more easily, and SOD1-immunopositive inclusions have been observed in the spinal cords of ALS patients. Because of this, SOD1 aggregation is thought to be related to the pathogenesis of ALS. Some core regions of amyloid have been identified, but the issue of whether these regions form aggregates in living cells remains unclear, and the mechanism responsible for intracellular SOD1 aggregation also remains unclear. The findings reported in this study indicate that the aggregation of the ALS-linked mutant SOD1-EGFP was significantly enhanced when the BioID2 gene was fused to the N-terminus of the mutant SOD1-EGFP plasmid for cellular expression. Expression of a series of BioID2-(C-terminal deletion peptides of SOD1)-EGFP permitted us to identify 1-35 as a minimal N-terminal sequence and Ile35 as an essential amino acid residue that contributes to the intracellular aggregation of SOD1. The findings also showed that an additional substitution of Ile35 with Ser into the ALS mutant SOD1 resulted in the significant suppression of aggregate formation. The fact that no Ile35 mutations have been reported to date in ALS patients indicates that all ALS mutant SOD1s contain Ile35. Taken together, we propose that Ile35 plays a pivotal role in the aggregation of the ALS-linked SOD1 and that this study will contribute to our understanding of the mechanism responsible for SOD1 aggregation.

Potential contribution of spinal interneurons to the etiopathogenesis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) consists of a group of adult-onset fatal and incurable neurodegenerative disorders characterized by the progressive death of motor neurons (MNs) throughout the central nervous system (CNS). At first, ALS was considered to be an MN disease, caused by cell-autonomous mechanisms acting specifically in MNs. Accordingly, data from ALS patients and ALS animal models revealed alterations in excitability in multiple neuronal populations, including MNs, which were associated with a variety of cellular perturbations such as protein aggregation, ribonucleic acid (RNA) metabolism defects, calcium dyshomeostasis, modified electrophysiological properties, and autophagy malfunctions. However, experimental evidence rapidly demonstrated the involvement of other types of cells, including glial cells, in the etiopathogenesis of ALS through non-cell autonomous mechanisms. Surprisingly, the contribution of pre-motor interneurons (INs), which regulate MN activity and could therefore critically modulate their excitability at the onset or during the progression of the disease, has to date been severely underestimated. In this article, we review in detail how spinal pre-motor INs are affected in ALS and their possible involvement in the etiopathogenesis of the disease.

How do we get from hyperexcitability to excitotoxicity in amyotrophic lateral sclerosis?

Amyotrophic lateral sclerosis is a devastating neurodegenerative disease that, at present, has no effective cure. Evidence of increased circulating glutamate and hyperexcitability of the motor cortex in patients with amyotrophic lateral sclerosis have provided an empirical support base for the 'dying forward' excitotoxicity hypothesis. The hypothesis postulates that increased activation of upper motor neurons spreads pathology to lower motor neurons in the spinal cord in the form of excessive glutamate release, which triggers excitotoxic processes. Many clinical trials have focused on therapies that target excitotoxicity via dampening neuronal activation, but not all are effective. As such, there is a growing tension between the rising tide of evidence for the 'dying forward' excitotoxicity hypothesis and the failure of therapies that target neuronal activation. One possible solution to these contradictory outcomes is that our interpretation of the current evidence requires revision in the context of appreciating the complexity of the nervous system and the limitations of the neurobiological assays we use to study it. In this review we provide an evaluation of evidence relevant to the 'dying forward' excitotoxicity hypothesis and by doing so, identify key gaps in our knowledge that need to be addressed. We hope to provide a road map from hyperexcitability to excitotoxicity so that we can better develop therapies for patients suffering from amyotrophic lateral sclerosis. We conclude that studies of upper motor neuron activity and their synaptic output will play a decisive role in the future of amyotrophic lateral sclerosis therapy.

The Cell Autonomous and Non-Cell Autonomous Aspects of Neuronal Vulnerability and Resilience in Amyotrophic Lateral Sclerosis

Simple Summary

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by a progressive paralysis due to the loss of particular neurons in our nervous system called motor neurons, that exert voluntary control of all our skeletal muscles. It is not entirely understood why motor neurons are particularly vulnerable in ALS, neither is it completely clear why certain groups of motor neurons, including those that regulate eye movement, are rather resilient to this disease. However, both vulnerability and resilience to ALS likely reflect cell intrinsic properties of different motor neuron subpopulations as well as non-cell autonomous events regulated by surrounding cell types. In this review we dissect the particular properties of different motor neuron types and their responses to disease that may underlie their respective vulnerabilities and resilience. Disease progression in ALS involves multiple cell types that are closely connected to motor neurons and we here also discuss their contributions to the differential vulnerability of motor neurons.

Abstract

Amyotrophic lateral sclerosis (ALS) is defined by the loss of upper motor neurons (MNs) that project from the cerebral cortex to the brain stem and spinal cord and of lower MNs in the brain stem and spinal cord which innervate skeletal muscles, leading to spasticity, muscle atrophy, and paralysis. ALS involves several disease stages, and multiple cell types show dysfunction and play important roles during distinct phases of disease initiation and progression, subsequently leading to selective MN loss. Why MNs are particularly vulnerable in this lethal disease is still not entirely clear. Neither is it fully understood why certain MNs are more resilient to degeneration in ALS than others. Brain stem MNs of cranial nerves III, IV, and VI, which innervate our eye muscles, are highly resistant and persist until the end-stage of the disease, enabling paralyzed patients to communicate through ocular tracking devices. MNs of the Onuf’s nucleus in the sacral spinal cord, that innervate sphincter muscles and control urogenital functions, are also spared throughout the disease. There is also a differential vulnerability among MNs that are intermingled throughout the spinal cord, that directly relate to their physiological properties. Here, fast-twitch fatigable (FF) MNs, which innervate type IIb muscle fibers, are affected early, before onset of clinical symptoms, while slow-twitch (S) MNs, that innervate type I muscle fibers, remain longer throughout the disease progression. The resilience of particular MN subpopulations has been attributed to intrinsic determinants and multiple studies have demonstrated their unique gene regulation and protein content in health and in response to disease. Identified factors within resilient MNs have been utilized to protect more vulnerable cells. Selective vulnerability may also, in part, be driven by non-cell autonomous processes and the unique surroundings and constantly changing environment close to particular MN groups. In this article, we review in detail the cell intrinsic properties of resilient and vulnerable MN groups, as well as multiple additional cell types involved in disease initiation and progression and explain how these may contribute to the selective MN resilience and vulnerability in ALS.

Motor neuron TDP-43 proteinopathy in progressive supranuclear palsy and corticobasal degeneration

Transactive response DNA-binding protein 43 kDa (TDP-43) is mislocalized from the nucleus and aggregates within the cytoplasm of affected neurons in amyotrophic lateral sclerosis (ALS) cases. TDP-43 pathology has also been found in brain tissues under non-ALS conditions, suggesting mechanistic links between TDP-43-related ALS (ALS-TDP) and various neurological disorders. This study aimed to assess TDP-43 pathology in the spinal cord motor neurons of tauopathies. We examined 106 spinal cords from consecutively autopsied cases with progressive supranuclear palsy (PSP, n = 26), corticobasal degeneration (CBD, n = 12), globular glial tauopathy (GGT, n = 5), Alzheimer's disease (AD, n = 21), or Pick disease (PiD, n = 6) and neurologically healthy controls (n = 36). Ten of the PSP cases (38%) and seven of the CBD cases (58%) showed mislocalization and cytoplasmic aggregation of TDP-43 in spinal cord motor neurons, which was prominent in the cervical cord. TDP-43-aggregates were found to be skein-like, round-shaped, granular, or dot-like and contained insoluble C-terminal fragments showing blotting pattern of ALS or frontotemporal lobar degeneration (FTLD). The lower motor neurons also showed cystatin-C aggregates, although Bunina bodies were absent in hematoxylin-eosin staining. The spinal cord TDP-43 pathology was often associated with TDP-43 pathology of the primary motor cortex. Positive correlations were shown between the severities of TDP-43 and 4-repeat (4R)-tau aggregates in the cervical cord. TDP-43 and 4R-tau aggregates burdens positively correlated with microglial burden in anterior horn. TDP-43 pathology of spinal cord motor neuron did not develop in an age-dependent manner and was not found in the AD, PiD, GGT, and control groups. Next, we assessed splicing factor proline/glutamine rich (SFPQ) expression in spinal cord motor neurons; SFPQ is a recently-identified regulator of ALS/FTLD pathogenesis, and it is also reported that interaction between SFPQ and fused-in-sarcoma (FUS) regulates splicing of microtubule-associated protein tau exon 10. Immunofluorescent and proximity-ligation assays revealed altered SFPQ/FUS-interactions in the neuronal nuclei of PSP, CBD, and ALS-TDP cases but not in AD, PiD, and GGT cases. Moreover, SFPQ expression was depleted in neurons containing TDP-43 or 4R-tau aggregates of PSP and CBD cases. Our results indicate that PSP and CBD may have properties of systematic motor neuron TDP-43 proteinopathy, suggesting mechanistic links with ALS-TDP. SFPQ dysfunction, arising from altered interaction with FUS, may be a candidate of the common pathway.

Ultrastructural characterization of peripheral denervation in a mouse model of Type III spinal muscular atrophy

Spinal muscular atrophy (SMA) is a heritable, autosomal recessive neuromuscular disorder characterized by a loss of the survival of motor neurons (SMN) protein, which leads to degeneration of lower motor neurons, and muscle atrophy. Despite SMA being nosographically classified as a motor neuron disease, recent advances indicate that peripheral alterations at the level of the neuromuscular junction (NMJ), involving the muscle, and axons of the sensory-motor system, occur early, and may even precede motor neuron loss. In the present study, we used a mouse model of slow progressive (type III) SMA, whereby the absence of the mouse SMN protein is compensated by the expression of two human genes (heterozygous SMN1A2G, and SMN2). This leads to late disease onset and prolonged survival, which allows for dissecting slow degenerative steps operating early in SMA pathogenesis. In this purely morphological study carried out at transmission electron microscopy, we extend the examination of motor neurons and proximal axons towards peripheral components, including distal axons, muscle fibers, and also muscle spindles. We document remarkable ultrastructural alterations being consistent with early peripheral denervation in SMA, which may shift the ultimate anatomical target in neuromuscular disease from the spinal cord towards the muscle. This concerns mostly mitochondrial alterations within distal axons and muscle, which are quantified here through ultrastructural morphometry. The present study is expected to provide a deeper knowledge of early pathogenic mechanisms in SMA.

How Degeneration of Cells Surrounding Motoneurons Contributes to Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by the progressive degeneration of upper and lower motoneurons. Despite motoneuron death being recognized as the cardinal event of the disease, the loss of glial cells and interneurons in the brain and spinal cord accompanies and even precedes motoneuron elimination. In this review, we provide striking evidence that the degeneration of astrocytes and oligodendrocytes, in addition to inhibitory and modulatory interneurons, disrupt the functionally coherent environment of motoneurons. We discuss the extent to which the degeneration of glial cells and interneurons also contributes to the decline of the motor system. This pathogenic cellular network therefore represents a novel strategic field of therapeutic investigation.

Effect of Basketball Sports on Serum Superoxide Dismutase and Its Relationship with the Nanoparticle Drug Delivery System

Human survival is impossible without oxygen, and as the body load continues to increase, the need for oxygen intake becomes greater. However, oxygen is also a double-edged sword for the human body. A large number of studies have proved that excessive intake of oxygen might lead to oxygen poisoning. Even under normal oxygen uptake, there is still a certain proportion of SOD conversion in oxygen. Superoxide dismutase (SOD) is one of the main causes of oxygen poisoning and chronic diseases. It is of great significance to study the changes of SOD in a large amount of oxygen environment. However, there are a few research studies in this field at home and abroad. Therefore, this paper puts forward the influence of basketball sports on serum superoxide dismutase (SOD) and its relationship with the nanoparticle drug delivery system. The research of this paper is mainly divided into three parts. The first part is the research of theoretical basis and core concepts. Through this part of the study, this paper shows that exercise can make the human body strong, while controlling the transformation of SOD, and only in this way can we achieve the true meaning of sports health. The second part is the establishment method of the test model of the influence of basketball on SOD and the nanoparticle drug delivery system. In this part, the principle and operation steps of the design method are given in detail. In order to ensure the effect of the experiment, the test standard was established, and the whole process data were recorded for the retrospective study. The third part is the comparative experiment, which includes the influence of different exercise intensities on SOD activity and the preservation stability of nanoparticles. Through the analysis of experimental data, it was found that basketball increased the risk of SOD transformation, but at the same time, using nanoparticles intervention can effectively reduce the harm of SOD to the human body.

Distinct roles for motor neuron autophagy early and late in the SOD1G93A mouse model of ALS

Mutations in autophagy genes can cause familial and sporadic amyotrophic lateral sclerosis (ALS). However, the role of autophagy in ALS pathogenesis is poorly understood, in part due to the lack of cell type-specific manipulations of this pathway in animal models. Using a mouse model of ALS expressing mutant superoxide dismutase 1 (SOD1^G93A), we show that motor neurons form large autophagosomes containing ubiquitinated aggregates early in disease progression. To investigate whether this response is protective or detrimental, we generated mice in which the critical autophagy gene Atg7 was specifically disrupted in motor neurons (Atg7 cKO). Atg7 cKO mice were viable but exhibited structural and functional defects at a subset of vulnerable neuromuscular junctions. By crossing Atg7 cKO mice to the SOD1^G93A mouse model, we found that autophagy inhibition accelerated early neuromuscular denervation of the tibialis anterior muscle and the onset of hindlimb tremor. Surprisingly, however, lifespan was extended in Atg7 cKO; SOD1^G93A double-mutant mice. Autophagy inhibition did not prevent motor neuron cell death, but it reduced glial inflammation and blocked activation of the stress-related transcription factor c-Jun in spinal interneurons. We conclude that motor neuron autophagy is required to maintain neuromuscular innervation early in disease but eventually acts in a non-cell-autonomous manner to promote disease progression.

A transgenic mouse expressing CHMP2Bintron5 mutant in neurons develops histological and behavioural features of amyotrophic lateral sclerosis and frontotemporal dementia

Mutations in the charged multivesicular body protein 2B (CHMP2B) are associated with frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS), and with a mixed ALS-FTD syndrome. To model this syndrome, we generated a transgenic mouse line expressing the human CHMP2B^intron5 mutant in a neuron-specific manner. These mice developed a dose-dependent disease phenotype. A longitudinal study revealed progressive gait abnormalities, reduced muscle strength and decreased motor coordination. CHMP2B^intron5 mice died due to generalized paralysis. When paralyzed, signs of denervation were present as attested by altered electromyographic profiles, by decreased number of fully innervated neuromuscular junctions, by reduction in size of motor endplates and by a decrease of sciatic nerve axons area. However, spinal motor neurons cell bodies were preserved until death. In addition to the motor dysfunctions, CHMP2B^intron5 mice progressively developed FTD-relevant behavioural modifications such as disinhibition, stereotypies, decrease in social interactions, compulsivity and change in dietary preferences. Furthermore, neurons in the affected spinal cord and brain regions showed accumulation of p62-positive cytoplasmic inclusions associated or not with ubiquitin and CHMP2B^intron5 As observed in FTD3 patients, these inclusions were negative for TDP-43 and FUS. Moreover, astrogliosis and microgliosis developed with age. Altogether, these data indicate that the neuronal expression of human CHMP2B^intron5 in areas involved in motor and cognitive functions induces progressive motor alterations associated with dementia symptoms and with histopathological hallmarks reminiscent of both ALS and FTD.

ALS mouse model SOD1G93A displays early pathology of sensory small fibers associated to accumulation of a neurotoxic splice variant of peripherin

Growing evidence suggests that amyotrophic lateral sclerosis (ALS) is a multisystem neurodegenerative disease that primarily affects motor neurons and, though less evidently, other neuronal systems. About 75% of sporadic and familial ALS patients show a subclinical degeneration of small-diameter fibers, as measured by loss of intraepidermal nerve fibers (IENFs), but the underlying biological causes are unknown. Small-diameter fibers are derived from small-diameter sensory neurons, located in dorsal root ganglia (DRG), whose biochemical hallmark is the expression of type III intermediate filament peripherin. We tested here the hypothesis that small-diameter DRG neurons of ALS mouse model SOD1(G93A)suffer from axonal stress and investigated the underlying molecular mechanism. We found that SOD1(G93A)mice display small fiber pathology, as measured by IENF loss, which precedes the onset of the disease. In vitro small-diameter DRG neurons of SOD1(G93A)mice show axonal stress features and accumulation of a peripherin splice variant, named peripherin56, which causes axonal stress through disassembling light and medium neurofilament subunits (NFL and NFM, respectively). Our findings first demonstrate that small-diameter DRG neurons of the ALS mouse model SOD1(G93A)display axonal stress in vitro and in vivo, thus sustaining the hypothesis that the effects of ALS disease spread beyond motor neurons. These results suggest a molecular mechanism for the small fiber pathology found in ALS patients. Finally, our data agree with previous findings, suggesting a key role of peripherin in the ALS pathogenesis, thus highlighting that DRG neurons mirror some dysfunctions found in motor neurons.

Inhibitory dysfunction in amyotrophic lateral sclerosis: future therapeutic opportunities

In amyotrophic lateral sclerosis, motor neuron hyperexcitability and inhibitory dysfunction is emerging as a potential causative link in the dysfunction and degeneration of the motoneuronal circuitry that characterizes the disease. Interneurons, as key regulators of excitability, may mediate much of this imbalance, yet we know little about the way in which inhibitory deficits perturb excitability. In this review, we explore inhibitory control of excitability and the potential contribution of altered inhibition to amyotrophic lateral sclerosis disease processes and vulnerabilities, identifying important windows of therapeutic opportunity and potential interventions, specifically targeting inhibitory control at key disease stages.

Compartment-dependent mitochondrial alterations in experimental ALS, the effects of mitophagy and mitochondriogenesis

Amyotrophic lateral sclerosis (ALS) is characterized by massive loss of motor neurons. Data from ALS patients and experimental models indicate that mitochondria are severely damaged within dying or spared motor neurons. Nonetheless, recent data indicate that mitochondrial preservation, although preventing motor neuron loss, fails to prolong lifespan. On the other hand, the damage to motor axons plays a pivotal role in determining both lethality and disease course. Thus, in the present article each motor neuron compartment (cell body, central, and peripheral axons) of G93A SOD-1 mice was studied concerning mitochondrial alterations as well as other intracellular structures. We could confirm the occurrence of ALS-related mitochondrial damage encompassing total swelling, matrix dilution and cristae derangement along with non-pathological variations of mitochondrial size and number. However, these alterations occur to a different extent depending on motor neuron compartment. Lithium, a well-known autophagy inducer, prevents most pathological changes. However, the efficacy of lithium varies depending on which motor neuron compartment is considered. Remarkably, some effects of lithium are also evident in wild type mice. Lithium is effective also in vitro, both in cell lines and primary cell cultures from the ventral spinal cord. In these latter cells autophagy inhibition within motor neurons in vitro reproduced ALS pathology which was reversed by lithium. Muscle and glial cells were analyzed as well. Cell pathology was mostly severe within peripheral axons and muscles of ALS mice. Remarkably, when analyzing motor axons of ALS mice a subtotal clogging of axoplasm was described for the first time, which was modified under the effects of lithium. The effects induced by lithium depend on several mechanisms such as direct mitochondrial protection, induction of mitophagy and mitochondriogenesis. In this study, mitochondriogenesis induced by lithium was confirmed in situ by a novel approach using [2-³H]-adenosine.

A natural human IgM that binds to gangliosides is therapeutic in murine models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating, fatal neurological disease that primarily affects spinal cord anterior horn cells and their axons for which there is no treatment. Here we report the use of a recombinant natural human IgM that binds to the surface of neurons and supports neurite extension, rHIgM12, as a therapeutic strategy in murine models of human ALS. A single 200 µg intraperitoneal dose of rHIgM12 increases survival in two independent genetic-based mutant SOD1 mouse strains (SOD1G86R and SOD1G93A) by 8 and 10 days, delays the onset of neurological deficits by 16 days, delays the onset of weight loss by 5 days, and preserves spinal cord axons and anterior horn neurons. Immuno-overlay of thin layer chromatography and surface plasmon resonance show that rHIgM12 binds with high affinity to the complex gangliosides GD1a and GT1b. Addition of rHIgM12 to neurons in culture increases α-tubulin tyrosination levels, suggesting an alteration of microtubule dynamics. We previously reported that a single peripheral dose of rHIgM12 preserved neurological function in a murine model of demyelination with axon loss. Because rHIgM12 improves three different models of neurological disease, we propose that the IgM might act late in the cascade of neuronal stress and/or death by a broad mechanism.

Summary: A single peripheral dose of a recombinant natural human IgM increases lifespan and delays neurological deficits in mouse models of human ALS.

Trophic factors as modulators of motor neuron physiology and survival: implications for ALS therapy

Motor neuron physiology and development depend on a continuous and tightly regulated trophic support from a variety of cellular sources. Trophic factors guide the generation and positioning of motor neurons during every stage of the developmental process. As well, they are involved in axon guidance and synapse formation. Even in the adult spinal cord an uninterrupted trophic input is required to maintain neuronal functioning and protection from noxious stimuli. Among the trophic factors that have been demonstrated to participate in motor neuron physiology are vascular endothelial growth factor (VEGF), glial-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF) and insulin-like growth factor 1 (IGF-1). Upon binding to membrane receptors expressed in motor neurons or neighboring glia, these trophic factors activate intracellular signaling pathways that promote cell survival and have protective action on motor neurons, in both in vivo and in vitro models of neuronal degeneration. For these reasons these factors have been considered a promising therapeutic method for amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases, although their efficacy in human clinical trials have not yet shown the expected protection. In this minireview we summarize experimental data on the role of these trophic factors in motor neuron function and survival, as well as their mechanisms of action. We also briefly discuss the potential therapeutic use of the trophic factors and why these therapies may have not been yet successful in the clinical use.

Spinal inhibitory circuits and their role in motor neuron degeneration

In the spinal cord neuronal activity is controlled by the balance between excitatory and inhibitory neurotransmission, mediated mainly by the neurotransmitters glutamate and GABA/glycine, respectively. Alterations of this equilibrium have been associated with spinal motor neuron hyperexcitability and degeneration, which can be induced by excitotoxicity or by decreasing inhibitory neurotransmission. Here we review the ventral horn neuronal network and the possible involvement of inhibitory circuits in the mechanisms of degeneration of motor neurons characteristic of amyotrophic lateral sclerosis (ALS). Whereas glutamate mediated excitotoxicity seems to be an important factor, recent experimental and histopathological evidence argue in favor of a decreased activity of the inhibitory circuits controlling motor neuron excitability, mainly the recurrent inhibition exerted by Renshaw cells. A decreased Renshaw cell activity may be caused by cell loss or by a reduction of its inhibitory action secondary to a decreased excitation from cholinergic interneurons. Ultimately, inhibitory failure by either mechanism might lead to motor neuron degeneration, and this suggests inhibitory circuits and Renshaw cells as pharmacologic targets for ALS treatment.

RNA toxicity from the ALS/FTD C9ORF72 expansion is mitigated by antisense intervention

A hexanucleotide GGGGCC repeat expansion in the noncoding region of the C9ORF72 gene is the most common genetic abnormality in familial and sporadic amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The function of the C9ORF72 protein is unknown, as is the mechanism by which the repeat expansion could cause disease. Induced pluripotent stem cell (iPSC)-differentiated neurons from C9ORF72 ALS patients revealed disease-specific (1) intranuclear GGGGCCexp RNA foci, (2) dysregulated gene expression, (3) sequestration of GGGGCCexp RNA binding protein ADARB2, and (4) susceptibility to excitotoxicity. These pathological and pathogenic characteristics were confirmed in ALS brain and were mitigated with antisense oligonucleotide (ASO) therapeutics to the C9ORF72 transcript or repeat expansion despite the presence of repeat-associated non-ATG translation (RAN) products. These data indicate a toxic RNA gain-of-function mechanism as a cause of C9ORF72 ALS and provide candidate antisense therapeutics and candidate human pharmacodynamic markers for therapy.

Amyotrophic Lateral Sclerosis and Metabolomics: Clinical Implication and Therapeutic Approach

Amyotrophic lateral sclerosis (ALS) is one of the most common motor neurodegenerative disorders, primarily affecting upper and lower motor neurons in the brain, brainstem, and spinal cord, resulting in paralysis due to muscle weakness and atrophy. The majority of patients die within 3–5 years of symptom onset as a consequence of respiratory failure. Due to relatively fast progression of the disease, early diagnosis is essential. Metabolomics offer a unique opportunity to understand the spatiotemporal metabolic crosstalks through the assessment of body fluids and tissue. So far, one of the most challenging issues related to ALS is to understand the variation of metabolites in body fluids and CNS with the progression of disease. In this paper we will review the changes in metabolic profile in response to disease progression condition and also see the therapeutic implication of various drugs in ALS patients.

Delayed administration of VEGF rescues spinal motor neurons from death with a short effective time frame in excitotoxic experimental models in vivo

VEGF (vascular endothelial growth factor) prevents neuronal death in different models of ALS (amyotrophic lateral sclerosis), but few studies have addressed the efficacy of VEGF to protect motor neurons after the onset of symptoms, a critical point when considering VEGF as a potential therapeutic target for ALS. We studied the capability of VEGF to protect motor neurons after an excitotoxic challenge in two models of spinal neurodegeneration in rats induced by AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) administered either chronically with osmotic minipumps or acutely by microdialysis. VEGF was administered through osmotic minipumps in the chronic model or injected intracerebroventricularly in the acute model, and its effects were assessed by immunohistochemical and histological analyses and motor performance tests. In the chronic model, VEGF stopped the progression of the paralysis and protected motor neurons when administered after AMPA before the onset of the motor symptoms, whereas no protection was observed when administered after the onset. VEGF was also protective in the acute model, but with a short time window, since the protection was effective when administered 1 h but not 2 h after AMPA. Our results indicate that while VEGF has an indubitable neuroprotective effect, its therapeutic potential for halting or delaying the progression of motor neuron loss in ALS would likely have a short effective time frame.

Inhibitory synaptic regulation of motoneurons: a new target of disease mechanisms in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the third most common adult-onset neurodegenerative disease. It causes the degeneration of motoneurons and is fatal due to paralysis, particularly of respiratory muscles. ALS can be inherited, and specific disease-causing genes have been identified, but the mechanisms causing motoneuron death in ALS are not understood. No effective treatments exist for ALS. One well-studied theory of ALS pathogenesis involves faulty RNA editing and abnormal activation of specific glutamate receptors as well as failure of glutamate transport resulting in glutamate excitotoxicity; however, the excitotoxicity theory is challenged by the inability of anti-glutamate drugs to have major disease-modifying effects clinically. Nevertheless, hyperexcitability of upper and lower motoneurons is a feature of human ALS and transgenic (tg) mouse models of ALS. Motoneuron excitability is strongly modulated by synaptic inhibition mediated by presynaptic glycinergic and GABAergic innervations and postsynaptic glycine receptors (GlyR) and GABA(A) receptors; yet, the integrity of inhibitory systems regulating motoneurons has been understudied in experimental models, despite findings in human ALS suggesting that they may be affected. We have found in tg mice expressing a mutant form of human superoxide dismutase-1 (hSOD1) with a Gly93 → Ala substitution (G93A-hSOD1), causing familial ALS, that subsets of spinal interneurons degenerate. Inhibitory glycinergic innervation of spinal motoneurons becomes deficient before motoneuron degeneration is evident in G93A-hSOD1 mice. Motoneurons in these ALS mice also have insufficient synaptic inhibition as reflected by smaller GlyR currents, smaller GlyR clusters on their plasma membrane, and lower expression of GlyR1α mRNA compared to wild-type motoneurons. In contrast, GABAergic innervation of ALS mouse motoneurons and GABA(A) receptor function appear normal. Abnormal synaptic inhibition resulting from dysfunction of interneurons and motoneuron GlyRs is a new direction for unveiling mechanisms of ALS pathogenesis that could be relevant to new therapies for ALS.

Spinal inhibitory interneuron pathology follows motor neuron degeneration independent of glial mutant superoxide dismutase 1 expression in SOD1-ALS mice

Motor neuron degeneration and skeletal muscle denervation are hallmarks of amyotrophic lateral sclerosis (ALS), but other neuron populations and glial cells are also involved in ALS pathogenesis. We examined changes in inhibitory interneurons in spinal cords of the ALS model low-copy Gurney G93A-SOD1 (G1del) mice and found reduced expression of markers of glycinergic and GABAergic neurons, that is, glycine transporter 2 (GlyT2) and glutamic acid decarboxylase (GAD65/67), specifically in the ventral horns of clinically affected mice. There was also loss of GlyT2 and GAD67 messenger RNA-labeled neurons in the intermediate zone. Ubiquitinated inclusions appeared in interneurons before 20 weeks of age, that is, after their development in motor neurons but before the onset of clinical signs and major motor neuron degeneration, which starts from 25 weeks of age. Because mutant superoxide dismutase 1 (SOD1) in glia might contribute to the pathogenesis, we also examined neuron-specific G93A-SOD1 mice; they also had loss of inhibitory interneuron markers in ventral horns and ubiquitinated interneuron inclusions. These data suggest that, in mutant SOD1-associated ALS, pathological changes may spread from motor neurons to interneuronsin a relatively early phase of the disease, independent of the presence of mutant SOD1 in glia. The degeneration of spinal inhibitory interneurons may in turn facilitate degeneration of motor neurons and contribute to disease progression.

Persistent inward currents in spinal motoneurons: important for normal function but potentially harmful after spinal cord injury and in amyotrophic lateral sclerosis

Meaningful body movements depend on the interplay between synaptic inputs to motoneurons and their intrinsic properties. Injury and disease often alter either or both of these factors and cause motoneuron and movement dysfunction. The ability of the motoneuronal membrane to generate persistent inward currents (PICs) is especially potent in setting the intrinsic excitability of motoneurons and can drastically change the motoneuron output to a given input. In this article, we review the role of PICs in modulating the excitability of spinal motoneurons during health, and their contribution to motoneuron excitability after spinal cord injury (SCI) and in amyotrophic lateral sclerosis (ALS) leading to exaggerated long-lasting reflexes and muscle spasms, and contributing to neuronal degeneration, respectively.

Evidence from computer simulations for alterations in the membrane biophysical properties and dendritic processing of synaptic inputs in mutant superoxide dismutase-1 motoneurons

A critical step in improving our understanding of the development of amyotrophic lateral sclerosis (ALS) is to identify the factors contributing to the alterations in the excitability of motoneurons and assess their individual contributions. Here we investigated the early alterations in the passive electrical and morphological properties of neonatal spinal motoneurons that occur by 10 d after birth, long before disease onset. We identified some of the factors contributing to these alterations, and estimated their individual contributions. To achieve this goal, we undertook a computer simulation analysis using realistic morphologies of reconstructed wild-type (WT) and mutant superoxide dismutase-1 (mSOD1) motoneurons. Ion channel parameters of these models were then tuned to match the experimental data on electrical properties obtained from these same motoneurons. We found that the reduced excitability of mSOD1 models was accompanied with decreased specific membrane resistance by approximately 25% and efficacy of synaptic inputs (slow and fast) by 12-22%. Linearity of summation of synaptic currents was similar to WT. We also assessed the contribution of the alteration in dendritic morphology alone to this decreased excitability and found that it reduced the input resistance by 10% and the efficacy of synaptic inputs by 7-15%. Our results were also confirmed in models with dendritic active conductances. Our simulations indicated that the alteration in passive electrical properties of mSOD1 models resulted from concurrent alterations in their morphology and membrane biophysical properties, and consequently altered the motoneuronal dendritic processing of synaptic inputs. These results clarify new aspects of spinal motoneurons malfunction in ALS.

A role for copper in the toxicity of zinc-deficient superoxide dismutase to motor neurons in amyotrophic lateral sclerosis

In the 16 years since mutations to copper, zinc superoxide dismutase (SOD1) were first linked to familial amyotrophic lateral sclerosis (ALS), a multitude of apparently contradictory results have prevented any general consensus to emerge about the mechanism of toxicity. A decade ago, we showed that the loss of zinc from SOD1 results in the remaining copper in SOD1 to become extremely toxic to motor neurons in culture by a mechanism requiring nitric oxide. The loss of zinc causes SOD1 to become more accessible, more redox reactive, and a better catalyst of tyrosine nitration. Although SOD1 mutant proteins have a modestly reduced affinity for zinc, wild-type SOD1 can be induced to lose zinc by dialysis at slightly acidic pH. Our zinc-deficient hypothesis offers a compelling explanation for how mutant SOD1s have an increased propensity to become selectively toxic to motor neurons and also explains how wild-type SOD1 can be toxic in nonfamilial ALS patients. One critical prediction is that a therapeutic agent directed at zinc-deficient mutant SOD1 could be even more effective in treating sporadic ALS patients. Although transgenic mice experiments have yielded contradictory evidence to the zinc-deficient hypothesis, we will review more recent studies that support a role for copper in ALS. A more careful examination of the role of copper and zinc binding to SOD1 may help counter the growing disillusion in the ALS field about understanding the pathological role of SOD1.

Presynaptic regulation of astroglial excitatory neurotransmitter transporter GLT1

The neuron-astrocyte synaptic complex is a fundamental operational unit of the nervous system. Astroglia regulate synaptic glutamate, via neurotransmitter transport by GLT1/EAAT2. Astroglial mechanisms underlying this essential neuron-glial communication are not known. We now show that presynaptic terminals regulate astroglial synaptic functions, GLT1/EAAT2, via kappa B-motif binding phosphoprotein (KBBP), the mouse homolog of human heterogeneous nuclear ribonucleoprotein K (hnRNP K), which binds the GLT1/EAAT2 promoter. Neuron-stimulated KBBP is required for GLT1/EAAT2 transcriptional activation and is responsible for astroglial alterations in neural injury. Denervation of neuron-astrocyte signaling by corticospinal tract transection, ricin-induced motor neuron death, or neurodegeneration in amyotrophic lateral sclerosis all result in reduced astroglial KBBP expression and transcriptional dysfunction of astroglial transporter expression. Presynaptic elements dynamically coordinate normal astroglial function and also provide a fundamental signaling mechanism by which altered neuronal function and injury leads to dysregulated astroglia in CNS disease.

Glycinergic innervation of motoneurons is deficient in amyotrophic lateral sclerosis mice: a quantitative confocal analysis

Altered motoneuron excitability is involved in amyotrophic lateral sclerosis pathobiology. To test the hypothesis that inhibitory interneuron innervation of spinal motoneurons is abnormal in an amyotrophic lateral sclerosis mouse model, we measured GABAergic, glycinergic, and cholinergic immunoreactive terminals on spinal motoneurons in mice expressing a mutant form of human superoxide dismutase-1 with a Gly93-->Ala substitution (G93A-SOD1) and in controls at different ages. Glutamic acid decarboxylase, glycine transporter-2, and choline acetyltransferase were used as markers for GABAergic, glycinergic, and cholinergic terminals, respectively. Triple immunofluorescent labeling of boutons contacting motoneurons was visualized by confocal microscopy and analyzed quantitatively. Glycine transporter-2-bouton density on lateral motoneurons was decreased significantly in G93A-SOD1 mice compared with controls. This reduction was absent at 6 weeks of age but present in asymptomatic 8-week-old mice and worsened with disease progression from 12 to 14 weeks of age. Motoneurons lost most glycinergic innervation by 16 weeks of age (end-stage) when there was a significant decrease in the numbers of motoneurons and choline acetyltransferase-positive boutons. No significant differences in glutamic acid decarboxylase-bouton densities were found in G93A-SOD1 mice. Reduction of glycinergic innervation preceded mitochondrial swelling and vacuolization. Calbindin-positive Renshaw cell number was decreased significantly at 12 weeks of age in G93A-SOD1 mice. Thus, either the selective loss of inhibitory glycinergic regulation of motoneuron function or glycinergic interneuron degeneration contributes to motoneuron degeneration in amyotrophic lateral sclerosis.

Neonatal neuronal circuitry shows hyperexcitable disturbance in a mouse model of the adult-onset neurodegenerative disease amyotrophic lateral sclerosis

Distinguishing the primary from secondary effects and compensatory mechanisms is of crucial importance in understanding adult-onset neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). Transgenic mice that overexpress the G93A mutation of the human Cu-Zn superoxide dismutase 1 gene (hSOD1(G93A) mice) are a commonly used animal model of ALS. Whole-cell patch-clamp recordings from neurons in acute slice preparations from neonatal wild-type and hSOD1(G93A) mice were made to characterize functional changes in neuronal activity. Hypoglossal motoneurons (HMs) in postnatal day 4 (P4)-P10 hSOD1(G93A) mice displayed hyperexcitability, increased persistent Na(+) current (PC(Na)), and enhanced frequency of spontaneous excitatory and inhibitory transmission, compared with wild-type mice. These functional changes in neuronal activity are the earliest yet reported for the hSOD1(G93A) mouse, and are present 2-3 months before motoneuron degeneration and clinical symptoms appear in these mice. Changes in neuronal activity were not restricted to motoneurons: superior colliculus interneurons also displayed hyperexcitability and synaptic changes (P10-P12). Furthermore, in vivo viral-mediated GFP (green fluorescent protein) overexpression in hSOD1(G93A) HMs revealed precocious dendritic remodeling, and behavioral assays revealed transient neonatal neuromotor deficits compared with controls. These findings underscore the widespread and early onset of abnormal neural activity in this mouse model of the adult neurodegenerative disease ALS, and suggest that suppression of PC(Na) and hyperexcitability early in life might be one way to mitigate or prevent cell death in the adult CNS.

Functional alterations of the ubiquitin-proteasome system in motor neurons of a mouse model of familial amyotrophic lateral sclerosis

In familial and sporadic amyotrophic lateral sclerosis (ALS) and in rodent models of the disease, alterations in the ubiquitin-proteasome system (UPS) may be responsible for the accumulation of potentially harmful ubiquitinated proteins, leading to motor neuron death. In the spinal cord of transgenic mice expressing the familial ALS superoxide dismutase 1 (SOD1) gene mutation G93A (SOD1G93A), we found a decrease in constitutive proteasome subunits during disease progression, as assessed by real-time PCR and immunohistochemistry. In parallel, an increased immunoproteasome expression was observed, which correlated with a local inflammatory response due to glial activation. These findings support the existence of proteasome modifications in ALS vulnerable tissues. To functionally investigate the UPS in ALS motor neurons in vivo, we crossed SOD1G93A mice with transgenic mice that express a fluorescently tagged reporter substrate of the UPS. In double-transgenic Ub(G76V)-GFP /SOD1G93A mice an increase in Ub(G76V)-GFP reporter, indicative of UPS impairment, was detectable in a few spinal motor neurons and not in reactive astrocytes or microglia, at symptomatic stage but not before symptoms onset. The levels of reporter transcript were unaltered, suggesting that the accumulation of Ub(G76V)-GFP was due to deficient reporter degradation. In some motor neurons the increase of Ub(G76V)-GFP was accompanied by the accumulation of ubiquitin and phosphorylated neurofilaments, both markers of ALS pathology. These data suggest that UPS impairment occurs in motor neurons of mutant SOD1-linked ALS mice and may play a role in the disease progression.

Mitochondrial changes in motor neurons of homozygotes of leucine 126 TT deletion SOD1 transgenic mice

We investigated the time course of ultrastructural changes of mitochondria in the spinal cord of homozygotes of Leu126TTdel SOD1 (superoxide dismutase 1) with FLAG (signal sequence at the C-terminal protein) transgenic mice (DF-homo). Non-Tg mice and wild-type human SOD1 with FLAG epitope transgenic mice (WF) were investigated as controls for non-onset Tg mice. Expansion and vacuolation of the mitochondrial matrix was exhibited in motor neurons in the anterior horns of DF-homo Tg mice at the presymptomatic stage. Such mitochondrial degeneration became severe at the postsymptomatic stage. In contrast, expansion of the mitochondrial inner-membrane space was not evident even at the terminal stage. Microvacuoles of cytoplasm and fibrillar inclusions were rarely shown from the early symptomatic stage. WF mice showed expansion and vacuolation of the mitochondrial inner membrane space at old age. Non-Tgs showed no obvious change in mitochondria. Gold-labeled human SOD1 immunoreactivity showed small amount of gold deposits in the vacuolated mitochondria. These results suggest that the expansion and vacuolation of mitochondrial matrix in the spinal cord of DF-homo transgenic mice is the first pathological change, but that it is not directly caused by the aggregation of an abnormal human SOD1 protein in intermembrane space of mitochondria.

Gene profiling of skeletal muscle in an amyotrophic lateral sclerosis mouse model

Muscle atrophy is a major hallmark of amyotrophic lateral sclerosis (ALS), the most frequent adult-onset motor neuron disease. To define the full set of alterations in gene expression in skeletal muscle during the course of the disease, we used the G86R superoxide dismutase-1 transgenic mouse model of ALS and performed high-density oligonucleotide microarrays. We compared these data to those obtained by axotomy-induced denervation. A major set of gene regulations in G86R muscles resembled those of surgically denervated muscles, but many others appeared specific to the ALS condition. The first significant transcriptional changes appeared in a subpopulation of mice before the onset of overt clinical symptoms and motor neuron death. These early changes affected genes involved in detoxification (e.g., ALDH3, metallothionein-2, and thioredoxin-1) and regeneration (e.g., BTG1, RB1, and RUNX1) but also tissue degradation (e.g., C/EBPdelta and DDIT4) and cell death (e.g., ankyrin repeat domain-1, CDKN1A, GADD45alpha, and PEG3). Of particular interest, metallothionein-1 and -2, ATF3, cathepsin-Z, and galectin-3 genes appeared, among others, commonly regulated in both skeletal muscle (our present data) and spinal motor neurons (as previously reported) of paralyzed ALS mice. The importance of these findings is twofold. First, they designate the distal part of the motor unit as a primary site of disease. Second, they identify specific gene regulations to be explored in the search for therapeutic strategies that could alleviate disease before motor neuron death manifests clinically.

REVIEW ARTILCE: Cell therapy and stem cells in animal models of motor neuron disorders

Amyotrophic lateral sclerosis (ALS), spinal bulbar muscular atrophy (or Kennedy's disease), spinal muscular atrophy and spinal muscular atrophy with respiratory distress 1 are neurodegenerative disorders mainly affecting motor neurons and which currently lack effective therapies. Recent studies in animal models as well as primary and embryonic stem cell models of ALS, utilizing over-expression of mutated forms of Cu/Zn superoxide dismutase 1, have shown that motor neuron degeneration in these models is in part a non cell-autonomous event and that by providing genetically non-compromised supporting cells such as microglia or growth factor-excreting cells, onset can be delayed and survival increased. Using models of acute motor neuron injury it has been shown that embryonic stem cell-derived motor neurons implanted into the spinal cord can innervate muscle targets and improve functional recovery. Thus, a rationale exists for the development of cell therapies in motor neuron diseases aimed at either protecting and/or replacing lost motor neurons, interneurons as well as non-neuronal cells. This review evaluates approaches used in animal models of motor neuron disorders and their therapeutic relevance.

Motor neuron disease in transgenic mice with an H46R mutant SOD1 gene

Human familial amyotrophic lateral sclerosis with an H46R mutant Cu/Zn superoxide dismutase (SOD1) gene is characterized by initial muscle weakness and atrophy in the legs and a very long-term clinical course (approximately 15 years). Transgenic mice with this mutation generated in our laboratory occasionally showed aggregates in the anterior horns and axonal degeneration in all white matter sections of the spinal cord on plastic sections at the presymptomatic stages (12 and 16 weeks old), although conventional staining revealed no pathologic changes. At the symptomatic stages (20 and 24 weeks), loss of anterior horn neurons was observed. On plastic sections, aggregates were frequently seen not only in the anterior horns but also in the posterior horns and in all sections of white matter. Degenerated fibers were observed in the anterior and posterior roots as well as in white matter. Electron and immunoelectron microscopic observation revealed human SOD1- and ubiquitin-positive aggregates consisting of intermediate filaments in the anterior horn even from an early presymptomatic stage. Thus, H46R mutant SOD1 transgenic mice are characterized by widespread pathologic changes of the spinal cord that extend beyond the motor system, including many aggregates lacking vacuoles. The close pathologic similarity makes this animal model suitable for the investigation of human familial amyotrophic lateral sclerosis with the mutation.

Morphometric and topographical studies of small neurons in sporadic amyotrophic lateral sclerosis spinal gray matter

Little attention has been paid to the degeneration of small neurons in ALS spinal gray matter. The purpose of the present paper was to undertake morphometric and quantitative analysis of the spinal gray matter of 15 ALS patients and compare findings to those of five controls. A significant reduction of small neurons in the anteromedial and intermediate parts of the gray matter were detected in ALS spinal cords with diffuse myelin pallor in the ventral aspects of the anterolateral columns outside the corticospinal tracts, and the number of small neurons in these areas was decreased significantly depending on the intensity of the myelin pallor. There were no significant alterations in the number of small neurons in the corresponding areas of ALS spinal cords without diffuse myelin pallor or in those of controls. In the posterior parts of the gray matter, there were no significant differences in the number of small neurons among ALS patients and controls. These findings strongly suggest that diffuse myelin pallor in the ventral aspects of anterolateral columns in ALS spinal cords is derived from the degeneration of small neurons in the anteromedial and intermediate parts of the gray matter.

Amyotrophic lateral sclerosis-associated copper/zinc superoxide dismutase mutations preferentially reduce the repulsive charge of the proteins

We provide bioinformatical evidence that protein charge plays a key role in the disease mechanism of amyotrophic lateral sclerosis (ALS). Analysis of 100 ALS-associated mutations in copper/zinc superoxide dismutase (SOD1) shows that these are site-selective with a preference to decrease the proteins' net repulsive charge. For each SOD1 monomer this charge is normally -6. Because biomolecules as a rule maintain net negative charge to assure solubility in the cellular interior, the result lends support to the hypothesis of protein aggregation as an initiating event in the ALS pathogenesis. The strength of the preferential reduction of repulsive charge is higher in SOD1-associated ALS than in other inherited protein disorders.

Motor neuron degeneration in amyotrophic lateral sclerosis mutant superoxide dismutase-1 transgenic mice: mechanisms of mitochondriopathy and cell death

The mechanisms of human mutant superoxide dismutase-1 (mSOD1) toxicity to motor neurons (MNs) are unresolved. We show that MNs in G93A-mSOD1 transgenic mice undergo slow degeneration lacking similarity to apoptosis structurally and biochemically. It is characterized by somal and mitochondrial swelling and formation of DNA single-strand breaks prior to double-strand breaks occurring in nuclear and mitochondrial DNA. p53 and p73 are activated in degenerating MNs, but without nuclear import. The MN death is independent of activation of caspases-1, -3, and -8 or apoptosis-inducing factor within MNs, with a blockade of apoptosis possibly mediated by Aven up-regulation. MN swelling is associated with compromised Na,K-ATPase activity and aggregation. mSOD1 mouse MNs accumulate mitochondria from the axon terminals and generate higher levels of superoxide, nitric oxide, and peroxynitrite than MNs in control mice. Nitrated and aggregated cytochrome c oxidase subunit-I and alpha-synuclein as well as nitrated SOD2 accumulate in mSOD1 mouse spinal cord. Mitochondria in mSOD1 mouse MNs accumulate NADPH diaphorase and inducible nitric oxide synthase (iNOS)-like immunoreactivity, and iNOS gene deletion extends significantly the life span of G93A-mSOD1 mice. Prior to MN loss, spinal interneurons degenerate. These results identify novel mechanisms for mitochondriopathy and MN degeneration in amyotrophic lateral sclerosis (ALS) mice involving blockade of apoptosis, accumulation of MN mitochondria with enhanced toxic potential from distal terminals, NOS localization in MN mitochondria and peroxynitrite damage, and early degeneration of alpha-synuclein(+) interneurons. The data support roles for oxidative stress, protein nitration and aggregation, and excitotoxicity as participants in the process of MN degeneration caused by mSOD1.

Mitochondria in amyotrophic lateral sclerosis: a trigger and a target

Strong evidence shows that mitochondrial dysfunction is involved in amyotrophic lateral sclerosis (ALS), but despite the fact that mitochondria play a central role in excitotoxicity, oxidative stress and apoptosis, the intimate underlying mechanism linking mitochondrial defects to motor neuron degeneration in ALS still remains elusive. Morphological and functional abnormalities occur in mitochondria in ALS patients and related animal models, although their exact nature and extent are controversial. Recent studies postulate that the mislocalization in mitochondria of mutant forms of copper-zinc superoxide dismutase (SOD1), the only well-documented cause of familial ALS, may account for the toxic gain of function of the enzyme, and hence induce motor neuron death. On the other hand, mitochondrial dysfunction in ALS does not seem to be restricted only to motor neurons as it is also present in other tissues, particularly the skeletal muscle. The presence of this 'systemic' defect in energy metabolism associated with the disease is supported in skeletal muscle tissue by impaired mitochondrial respiration and overexpression of uncoupling protein 3. In addition, the lifespan of transgenic mutant SOD1 mice is increased by a highly energetic diet compensating both the metabolic defect and the motorneuronal function. In this review, we will focus on the mitochondrial dysfunction linked to ALS and the cause-and-effect relationships between mitochondria and the pathological mechanisms thought to be involved in the disease.

Neuroinformatics: a new tool for studying the brain

BACKGROUND

Central nervous system diseases constitute a major target for drug development. Genes expressed by the nervous system may represent half or more of the mammalian genome, with literally tens of thousands of gene products.

METHODS

Better methods are therefore required to accelerate the pace of mapping gene expression patterns in the mouse brain and to evaluate the progressive phenotypic changes in genetic models of human brain diseases.

CONCLUSIONS

Recent studies of mouse models of Amyotrophic Lateral Sclerosis and Alzheimer's disease illustrate how such data could be used for drug development. Since these two diseases-- especially Alzheimer's Disease-- entail disordered behavior, cognition and emotions, the framework and the methodology described in this article might in the future find applications in research on affective disorders.

Widespread loss of neuronal populations in the spinal ventral horn in sporadic motor neuron disease. A morphometric study

The cytopathology and loss of neurons was studied in 7670 neurons from the ventral horn of the third lumbar segment of the spinal cord of six sporadic motor neuron disease (MND) patients compared with 7568 neurons in seven age matched control subjects. A modified Tomlinson et al. [Tomlinson BE, Irving D, Rebeiz JJ. Total numbers of limb motor neurones in the human lumbosacral cord and an analysis of the accuracy of various sampling procedures. J Neurol Sci 1973;20:313-27] sampling procedure was used for neuronal counts. The ventral horn was divided in quadrants. Neuronal populations were also classified by the maximum cell diameter through the nucleolus. There was widespread loss of neurons in all quadrants of the ventral horn in MND. Size distribution histograms showed similar neuron loss across all populations of neurons. The dorsomedial quadrant contains almost exclusively interneurons and the ventrolateral quadrant mostly motor neurons. The cytopathology of neurons in the dorsomedial quadrant and of large motorneurons in the ventrolateral quadrant MND was similar. In the dorsomedial quadrant, neuron loss (56.7%) was similar to the loss of large motor neurons in the ventrolateral quadrant (64.4%). The loss of presumed motor neurons and interneurons increased with increased disease duration. There was no evidence that loss of presumed interneurons occurred prior, or subsequent, to loss of motor neurons. We conclude that, in sporadic MND, all neuronal populations in the ventral horn are affected and that interneurons are involved to a similar extent and in parallel with motor neurons, as reported in the G86R transgenic mouse model of familial MND. The increasing evidence of loss of neurons other than motor neurons in MND suggests the need for revising the concept of selective motor neuron vulnerability.

Early signs of motoneuron vulnerability in a disease model system: Characterization of transverse slice cultures of spinal cord isolated from embryonic ALS mice

Mutations in the SOD1 gene are associated with familial amyotrophic lateral sclerosis. The mechanisms by which these mutations lead to cell loss within the spinal cord ventral horns are unknown. In the present report we used the G93A transgenic mouse model of amyotrophic lateral sclerosis to develop and characterize an in vitro tool for the investigation of subtle alterations of spinal tissue prior to frank neuronal degeneration. To this aim, we developed organotypic slice cultures from wild type and G93A embryonic spinal cords. We combined immunocytochemistry and electron microscopy techniques to compare wild type and G93A spinal cord tissues after 14 days of growth under standard in vitro conditions. By SMI32 and choline acetyl transferase immunostaining, the distribution and morphology of motoneurons were compared in the two culture groups. Wild type and mutant cultures displayed no differences in the analyzed parameters as well as in the number of motoneurons. Similar results were observed when glial fibrillary acidic protein and myelin basic protein-positive cells were examined. Cell types within the G93A slice underwent maturation and slices could be maintained in culture for at least 3 weeks when prepared from embryos. Electron microscopy investigation confirmed the absence of early signs of mitochondria vacuolization or protein aggregate formation in G93A ventral horns. However, a significantly different ratio between inhibitory and excitatory synapses was present in G93A cultures, when compared with wild type ones, suggesting the expression of subtle synaptic dysfunction in G93A cultured tissue. When compared with controls, G93A motoneurons exhibited increased vulnerability to AMPA glutamate receptor-mediated excitotoxic stress prior to clear disease appearance. This in vitro disease model may thus represent a valuable tool to test early mechanisms contributing to motoneuron degeneration and potential therapeutic molecular interventions.

Regional and temporal alterations of ODC/polyamine system during ALS-like neurodegenerative motor syndrome in G93A transgenic mice

Natural polyamines (putrescine, spermidine and spermine) are ubiquitous molecules known to regulate a number of physiological processes and suspected to play a role also in various pathological conditions. Changes in polyamine levels and in their biosynthetic enzymes have been described for some neurodegenerative diseases but the available data are incomplete and somewhat contradictory. We report here alterations of the key enzyme of the polyamine pathway, ornithine decarboxylase (ODC) catalytic activity and polyamine levels in different CNS areas from SOD1 G39A transgenic mice, an animal model for amyotrophic lateral sclerosis (ALS). ODC catalytic activity, was found significantly increased both in the cervical and lumbar spinal cord and, to a lesser extent in the brain stem of transgenic mice at a symptomatic stage of the disease (125-day-old mice), while no differences were present at a pre-symptomatic stage (55-day-old mice). In parallel with the increase of ODC activity putrescine levels were several times increased in both cervical and lumbar spinal cord and in the brain stem of 125-day-old SOD1 G39A mice. Higher order polyamines were not increased except for a significant increase of spermidine in the cervical spinal cord. The present data demonstrate considerable alterations of the ODC/polyamine system in a reliable animal model of ASL, consistent with their role in neurodegeneration and in particular in motor neuron diseases.