Skeletal muscle-restricted expression of human SOD1 causes motor neuron degeneration in transgenic mice

Neuromuscular junction protection for the potential treatment of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease characterized by the progressive degeneration of upper and lower motor neurons (MNs), leading to muscular atrophy and eventual respiratory failure. ALS research has primarily focused on mechanisms regarding MN cell death; however, degenerative processes in the skeletal muscle, particularly involving neuromuscular junctions (NMJs), are observed in the early stages of and throughout disease progression. According to the "dying-back" hypothesis, NMJ degeneration may not only precede, but actively cause upper and lower MN loss. The importance of NMJ pathology has relatively received little attention in ALS, possibly because compensatory mechanisms mask NMJ loss for prolonged periods. Many mechanisms explaining NMJ degeneration have been proposed such as the disruption of anterograde/retrograde axonal transport, irregular cellular metabolism, and changes in muscle gene and protein expression. Neurotrophic factors, which are known to have neuroprotective and regenerative properties, have been intensely investigated for their therapeutic potential in both the preclinical and clinical setting. Additional research should focus on the potential of preserving NMJs in order to delay or prevent disease progression.

The complex molecular biology of amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder that causes selective death of motor neurons followed by paralysis and death. A subset of ALS cases is caused by mutations in the gene for Cu, Zn superoxide dismutase (SOD1), which impart a toxic gain of function to this antioxidant enzyme. This neurotoxic property is widely believed to stem from an increased propensity to misfold and aggregate caused by decreased stability of the native homodimer or a tendency to lose stabilizing posttranslational modifications. Study of the molecular mechanisms of SOD1-related ALS has revealed a complex array of interconnected pathological processes, including glutamate excitotoxicity, dysregulation of neurotrophic factors and axon guidance proteins, axonal transport defects, mitochondrial dysfunction, deficient protein quality control, and aberrant RNA processing. Many of these pathologies are directly exacerbated by misfolded and aggregated SOD1 and/or cytosolic calcium overload, suggesting the primacy of these events in disease etiology and their potential as targets for therapeutic intervention.

Analysis of neuromuscular junctions and effects of anabolic steroid administration in the SOD1G93A mouse model of ALS

Several lines of evidence indicate that neuromuscular junction (NMJ) destruction and disassembly is an early phenomenon in amyotrophic lateral sclerosis (ALS). Here we analyzed by confocal and electron microscopy the NMJ structure in the diaphragm of SOD1G93A mice at symptom onset. In these mice, which provide a model for familial ALS, diaphragm denervation (~50%) as well as gastrocnemius denervation (~40%) was found. In addition, the size of the synaptic vesicle pool was reduced and alterations of mitochondria were observed in approximately 40% of the remaining presynaptic terminals. Chronic treatment of SOD1G93A mice with the anabolic steroid nandrolone during the presymptomatic stage preserved the diaphragm muscle mass and features indicative of synaptic activity. These features were represented by the number of vesicles docked within 200 nm from the presynaptic membrane and area of acetylcholine receptor clusters. Structural preservation of mitochondria was documented in presynaptic terminals. However, innervation of diaphragm muscle fibers was only slightly increased in nandrolone-treated SOD1-mutant mice. Altogether the results point out and define fine structural alterations of diaphragm NMJs in the murine model of familial ALS at symptom onset, and indicate that nandrolone may prevent or delay structural alterations in NMJ mitochondria and stimulate presynaptic activity but does not prevent muscle denervation during the disease.

Differential gene expression in the axotomized facial motor nucleus of presymptomatic SOD1 mice

Previously, we compared molecular profiles of one population of wild-type (WT) mouse facial motoneurons (FMNs) surviving with FMNs undergoing significant cell death after axotomy. Regardless of their ultimate fate, injured FMNs respond with a vigorous pro-survival/regenerative molecular response. In contrast, the neuropil surrounding the two different injured FMN populations contained distinct molecular differences that support a causative role for glial and/or immune-derived molecules in directing contrasting responses of the same cell types to the same injury. In the current investigation, we utilized the facial nerve axotomy model and a presymptomatic amyotrophic lateral sclerosis (ALS) mouse (SOD1) model to experimentally mimic the axonal die-back process observed in ALS pathogenesis without the confounding variable of disease onset. Presymptomatic SOD1 mice had a significant decrease in FMN survival compared with WT, which suggests an increased susceptibility to axotomy. Laser microdissection was used to accurately collect uninjured and axotomized facial motor nuclei of WT and presymptomatic SOD1 mice for mRNA expression pattern analyses of pro-survival/pro-regeneration genes, neuropil-specific genes, and genes involved in or responsive to the interaction of FMNs and non-neuronal cells. Axotomized presymptomatic SOD1 FMNs displayed a dynamic pro-survival/regenerative response to axotomy, similar to WT, despite increased cell death. However, significant differences were revealed when the axotomy-induced gene expression response of presymptomatic SOD1 neuropil was compared with WT. We propose that the increased susceptibility of presymptomatic SOD1 FMNs to axotomy-induced cell death and, by extrapolation, disease progression, is not intrinsic to the motoneuron, but rather involves a dysregulated response by non-neuronal cells in the surrounding neuropil.

Defective neuromuscular transmission in the SOD1 G93A transgenic mouse improves after administration of human umbilical cord blood cells

To assess the effect of human umbilical cord blood (hUCB) transplantation on neuromuscular transmission in SOD1(G93A) transgenic mice, we studied the probability of neuromuscular transmission (PNMT), a relevant physiological indicator of motor nerve function, in 3 SOD1(G93A) mice transplanted with hUCB and compared to PNMT in 4 SOD1(G93A) mice without cell transplantation and 3 non-mutant SOD1 transgenic mice. For preparations isolated from non-mutant SOD1 transgenic mice, PNMT was 0.93 and 0.84 during the first 5 s of 70 and 90 Hz trains, respectively. PNMT gradually declined to 0.77 and 0.42 at the end of the trains. In striking contrast, PNMT for preparations from non-treated mutant SOD1(G93A) mice was 0.52 and 0.36 in the first 5 s of 70 and 90 Hz trains, respectively (p<0.05). Treatment with hUCB significantly (p<0.05) improved PNMT in SOD1(G93A) preparations. That is, the initial 5 s PNMT was 0.88 and 0.68 for the 70 and 90 Hz stimuli, respectively. We concluded that hUCB transplantation significantly improved PNMT for muscles removed from SOD1(G93A) mice. Testing PNMT in the SOD1(G93A) mouse model could be used as a simple in vitro protocol to detect a positive cellular response to therapeutic interventions in ALS.

Dihydrotestosterone ameliorates degeneration in muscle, axons and motoneurons and improves motor function in amyotrophic lateral sclerosis model mice

Amyotrophic lateral sclerosis (ALS) is a lethal disease characterized by a progressive loss of motoneurons. The clinical symptoms include skeletal muscle weakness and atrophy, which impairs motor performance and eventually leads to respiratory failure. We tested whether dihydrotestosterone (DHT), which has both anabolic effects on muscle and neuroprotective effects on axons and motoneurons, can ameliorate clinical symptoms in ALS. A silastic tube containing DHT crystals was implanted subcutaneously in SOD1-G93A mice at early symptomatic age when decreases in body weight and grip-strength were observed as compared to wild-type mice. DHT-treated SOD1-G93A mice demonstrated ameliorated muscle atrophy and increased body weight, which was associated with stronger grip-strength. DHT treatment increased the expression of insulin-like growth factor-1 in muscle, which can exert myotrophic as well as neurotrophic effects through retrograde transport. DHT treatment attenuated neuromuscular junction denervation, and axonal and motoneuron loss. DHT-treated SOD1-G93A mice demonstrated improvement in motor behavior as assessed by rota-rod and gait analyses, and an increased lifespan. Application of DHT is a relatively simple and non-invasive procedure, which may be translated into therapy to improve the quality of life for ALS patients.

Muscling in on PGC-1α for improved quality of life in ALS

Impaired activity of peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC)-1α has been implicated in the pathophysiology of several neurodegenerative disorders. In this issue, Da Cruz et al. (2012) show improved muscle function, but not survival, with increased PGC-1α activity in muscle in a mouse model of amyotrophic lateral sclerosis.

Elevated PGC-1α activity sustains mitochondrial biogenesis and muscle function without extending survival in a mouse model of inherited ALS

The transcriptional coactivator PGC-1α induces multiple effects on muscle, including increased mitochondrial mass and activity. Amyotrophic lateral sclerosis (ALS) is a progressive, fatal, adult-onset neurodegenerative disorder characterized by selective loss of motor neurons and skeletal muscle degeneration. An early event is thought to be denervation-induced muscle atrophy accompanied by alterations in mitochondrial activity and morphology within muscle. We now report that elevation of PGC-1α levels in muscles of mice that develop fatal paralysis from an ALS-causing SOD1 mutant elevates PGC-1α-dependent pathways throughout disease course. Mitochondrial biogenesis and activity are maintained through end-stage disease, accompanied by retention of muscle function, delayed muscle atrophy, and significantly improved muscle endurance even at late disease stages. However, survival was not extended. Therefore, muscle is not a primary target of mutant SOD1-mediated toxicity, but drugs increasing PGC-1α activity in muscle represent an attractive therapy for maintaining muscle function during progression of ALS.

Roadmap and standard operating procedures for biobanking and discovery of neurochemical markers in ALS

Despite major advances in deciphering the neuropathological hallmarks of amyotrophic lateral sclerosis (ALS), validated neurochemical biomarkers for monitoring disease activity, earlier diagnosis, defining prognosis and unlocking key pathophysiological pathways are lacking. Although several candidate biomarkers exist, translation into clinical application is hindered by small sample numbers, especially longitudinal, for independent verification. This review considers the potential routes to the discovery of neurochemical markers in ALS, and provides a consensus statement on standard operating procedures that will facilitate multicenter collaboration, validation and ultimately clinical translation.

Mitochondrial pathobiology in ALS

Amyotrophic lateral sclerosis (ALS) is the third most common human adult-onset neurodegenerative disease. Some forms of ALS are inherited, and disease-causing genes have been identified. Nevertheless, the mechanisms of neurodegeneration in ALS are unresolved. Genetic, biochemical, and morphological analyses of human ALS as well as cell and animal models of ALS reveal that mitochondria could have roles in this neurodegeneration. The varied functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress and overlying genetic variations. Changes occur in mitochondrial respiratory chain enzymes and mitochondrial programmed cell death proteins in ALS. Transgenic mouse models of ALS reveal possible principles governing the biology of neurodegeneration that implicate mitochondria and the mitochondrial permeability transition pore. This paper reviews how mitochondrial pathobiology might contribute to the mechanisms of neurodegeneration in ALS.

Nuclear localization of human SOD1 and mutant SOD1-specific disruption of survival motor neuron protein complex in transgenic amyotrophic lateral sclerosis mice

Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset neurodegenerative disease that causes degeneration of motor neurons and paralysis. Approximately 20% of familial ALS cases have been linked to mutations in the copper/zinc superoxide dismutase (SOD1) gene, but it is unclear how mutations in the protein result in motor neuron degeneration. Transgenic (tg) mice expressing mutated forms of human SOD1 (hSOD1) develop clinical and pathological features similar to those of ALS. We used tg mice expressing hSOD1-G93A, hSOD1-G37R, and hSOD1-wild-type to investigate a new subcellular pathology involving mutant hSOD1 protein prominently localizing to the nuclear compartment and disruption of the architecture of nuclear gems. We developed methods for extracting relatively pure cell nucleus fractions from mouse CNS tissues and demonstrate a low nuclear presence of endogenous SOD1 in mouse brain and spinal cord, but prominent nuclear accumulation of hSOD1-G93A, -G37R, and -wild-type in tg mice. The hSOD1 concentrated in the nuclei of spinal cord cells, particularly motor neurons, at a young age. The survival motor neuron protein (SMN) complex is disrupted in motor neuron nuclei before disease onset in hSOD1-G93A and -G37R mice; age-matched hSOD1-wild-type mice did not show SMN disruption despite a nuclear presence. Our data suggest new mechanisms involving hSOD1 accumulation in the cell nucleus and mutant hSOD1-specific perturbations in SMN localization with disruption of the nuclear SMN complex in ALS mice and suggest an overlap of pathogenic mechanisms with spinal muscular atrophy.

Neurogenic and myogenic contributions to hereditary motor neuron disease

Spinal muscular atrophy and spinal and bulbar muscular atrophy are characterized by lower motor neuron loss and muscle atrophy. Although it is accepted that motor neuron loss is a primary event in disease pathogenesis, inherent defects in muscle may also contribute to the disease progression and severity. In this review, we discuss the relative contributions of primary pathological processes in the motor axons, neuromuscular junctions and muscle to disease manifestations. Characterizing these contributions helps us to better understand the disease mechanisms and to better target therapeutic intervention.

Using induced pluripotent stem cells (iPSC) to model human neuromuscular connectivity: promise or reality?

Motor neuron diseases (MND) such as amyotrophic lateral sclerosis and spinal muscular atrophy are devastating, progressive and ultimately fatal diseases for which there are no effective treatments. Recent evidence from systematic studies of animal models and human patients suggests that the neuromuscular junction (NMJ) is an important early target in MND, demonstrating functional and structural abnormalities in advance of pathological changes occurring in the motor neuron cell body. The ability to study pathological changes occurring at the NMJ in humans is therefore likely to be important for furthering our understanding of disease pathogenesis, and also for designing and testing new therapeutics. However, there are many practical and technical reasons why it is not possible to visualise or record from NMJs in pre- and early-symptomatic MND patients in vivo. Other approaches are therefore required. The development of stem cell technologies has opened up the possibility of creating human NMJs in vitro, using pluripotent cells generated from healthy individuals and patients with MND. This review covers historical attempts to develop mature and functional NMJs in vitro, using co-cultures of muscle and nerve from animals, and discusses how recent developments in the generation and specification of human induced pluripotent stem cells provides an opportunity to build on these previous successes to recapitulate human neuromuscular connectivity in vitro.

Epigenetic regulation of motor neuron cell death through DNA methylation

DNA methylation is an epigenetic mechanism for gene silencing engaged by DNA methyltransferase (Dnmt)-catalyzed methyl group transfer to cytosine residues in gene-regulatory regions. It is unknown whether aberrant DNA methylation can cause neurodegeneration. We tested the hypothesis that Dnmts can mediate neuronal cell death. Enforced expression of Dnmt3a induced degeneration of cultured NSC34 cells. During apoptosis of NSC34 cells induced by camptothecin, levels of Dnmt1 and Dnmt3a increased fivefold and twofold, respectively, and 5-methylcytosine accumulated in nuclei. Truncation mutation of the Dnmt3a catalytic domain and Dnmt3a RNAi blocked apoptosis of cultured neurons. Inhibition of Dnmt catalytic activity with RG108 and procainamide protected cultured neurons from excessive DNA methylation and apoptosis. In vivo, Dnmt1 and Dnmt3a are expressed differentially during mouse brain and spinal cord maturation and in adulthood when Dnmt3a is abundant in synapses and mitochondria. Dnmt1 and Dnmt3a are expressed in motor neurons of adult mouse spinal cord, and, during their apoptosis induced by sciatic nerve avulsion, nuclear and cytoplasmic 5-methylcytosine immunoreactivity, Dnmt3a protein levels and Dnmt enzyme activity increased preapoptotically. Inhibition of Dnmts with RG108 blocked completely the increase in 5-methycytosine and the apoptosis of motor neurons in mice. In human amyotrophic lateral sclerosis (ALS), motor neurons showed changes in Dnmt1, Dnmt3a, and 5-methylcytosine similar to experimental models. Thus, motor neurons can engage epigenetic mechanisms to drive apoptosis, involving Dnmt upregulation and increased DNA methylation. These cellular mechanisms could be relevant to human ALS pathobiology and disease treatment.

Biology of mitochondria in neurodegenerative diseases

Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) are the most common human adult-onset neurodegenerative diseases. They are characterized by prominent age-related neurodegeneration in selectively vulnerable neural systems. Some forms of AD, PD, and ALS are inherited, and genes causing these diseases have been identified. Nevertheless, the mechanisms of the neuronal degeneration in these familial diseases, and in the more common idiopathic (sporadic) diseases, are unresolved. Genetic, biochemical, and morphological analyses of human AD, PD, and ALS, as well as their cell and animal models, reveal that mitochondria could have roles in this neurodegeneration. The varied functions and properties of mitochondria might render subsets of selectively vulnerable neurons intrinsically susceptible to cellular aging and stress and the overlying genetic variations. In AD, alterations in enzymes involved in oxidative phosphorylation, oxidative damage, and mitochondrial binding of Aβ and amyloid precursor protein have been reported. In PD, mutations in mitochondrial proteins have been identified and mitochondrial DNA mutations have been found in neurons in the substantia nigra. In ALS, changes occur in mitochondrial respiratory chain enzymes and mitochondrial programmed cell death proteins. Transgenic mouse models of human neurodegenerative disease are beginning to reveal possible principles governing the biology of selective neuronal vulnerability that implicate mitochondria and the mitochondrial permeability transition pore. This chapter reviews several aspects of mitochondrial biology and how mitochondrial pathobiology might contribute to the mechanisms of neurodegeneration in AD, PD, and ALS.

Promotion of plasma membrane repair by vitamin E

Severe vitamin E deficiency results in lethal myopathy in animal models. Membrane repair is an important myocyte response to plasma membrane disruption injury as when repair fails, myocytes die and muscular dystrophy ensues. Here we show that supplementation of cultured cells with α-tocopherol, the most common form of vitamin E, promotes plasma membrane repair. Conversely, in the absence of α-tocopherol supplementation, exposure of cultured cells to an oxidant challenge strikingly inhibits repair. Comparative measurements reveal that, to promote repair, an anti-oxidant must associate with membranes, as α-tocopherol does, or be capable of α-tocopherol regeneration. Finally, we show that myocytes in intact muscle cannot repair membranes when exposed to an oxidant challenge, but show enhanced repair when supplemented with vitamin E. Our work suggests a novel biological function for vitamin E in promoting myocyte plasma membrane repair. We propose that this function is essential for maintenance of skeletal muscle homeostasis.

Membrane repair of myocytes is important to prevent such disease as muscular dystrophy but the properties of this repair are not well characterised. In this study, vitamin E is shown to be important in the repair of myocyte cell membranes in cultured cells and in intact muscle.

Gender-Specific Mechanism of Synaptic Impairment and Its Prevention by GCSF in a Mouse Model of ALS

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease of motoneurons which progresses differentially in males and females for unknown reason. Here we measured gender differences in pre- and post-synaptic parameters of the neuromuscular transmission in a mutant G93A-SOD1 mouse model of ALS. Using intracellular microelectrode technique we recorded miniature and evoked end-plate potentials (MEPPs and EPPs) in the diaphragm muscle of G93A-SOD1 mice at early symptomatic stage. While no evident alterations in the amplitude of MEPPs was observed in male or female G93A-SOD1 mice, G93A-SOD1 mice displayed dramatically reduced probability of spontaneous acetylcholine release. In contrast, the EPPs evoked by single nerve stimulation had unchanged amplitude and quantal content. In males, but not females, this was accompanied by reduced readily releasable transmitter pool. Transmitter release in both sexes was sensitive to the inhibitory action of reactive oxygen species (ROS), but the production of ROS was increased in the spinal cords of male but not female G93A-SOD1 mice. Treatment with granulocyte colony stimulating factor (GCSF), which we previously found to be beneficial in males, attenuated the increased ROS production indicating involvement of the antioxidant mechanisms and improved ALS-induced synaptic dysfunctions only in males being ineffective in females. Consistent with our findings at synaptic level, GCSF did not change the survival rate or motor performance of female ALS mice. In summary, neuromuscular transmission in ALS mice is impaired at early symptomatic stage when a dramatic presynaptic decline of spontaneous release occurs. Beneficial effects of GCSF treatment on survival in males may be explained by GCSF-improved presynaptic functions in male G93A-SOD1 mice. Development of efficient treatment strategies for ALS may need to be directed in a gender-specific manner.

The anabolic/androgenic steroid nandrolone exacerbates gene expression modifications induced by mutant SOD1 in muscles of mice models of amyotrophic lateral sclerosis

Anabolic/androgenic steroids (AAS) are drugs that enhance muscle mass, and are often illegally utilized in athletes to improve their performances. Recent data suggest that the increased risk for amyotrophic lateral sclerosis (ALS) in male soccer and football players could be linked to AAS abuse. ALS is a motor neuron disease mainly occurring in sporadic (sALS) forms, but some familial forms (fALS) exist and have been linked to mutations in different genes. Some of these, in their wild type (wt) form, have been proposed as risk factors for sALS, i.e. superoxide dismutase 1 (SOD1) gene, whose mutations are causative of about 20% of fALS. Notably, SOD1 toxicity might occur both in motor neurons and in muscle cells. Using gastrocnemius muscles of mice overexpressing human mutant SOD1 (mutSOD1) at different disease stages, we found that the expression of a selected set of genes associated to muscle atrophy, MyoD, myogenin, atrogin-1, and transforming growth factor (TGF)β1, is up-regulated already at the presymptomatic stage. Atrogin-1 gene expression was increased also in mice overexpressing human wtSOD1. Similar alterations were found in axotomized mouse muscles and in cultured ALS myoblast models. In these ALS models, we then evaluated the pharmacological effects of the synthetic AAS nandrolone on the expression of the genes modified in ALS muscle. Nandrolone administration had no effects on MyoD, myogenin, and atrogin-1 expression, but it significantly increased TGFβ1 expression at disease onset. Altogether, these data suggest that, in fALS, muscle gene expression is altered at early stages, and AAS may exacerbate some of the alterations induced by SOD1 possibly acting as a contributing factor also in sALS.

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.

Amyotrophic lateral sclerosis multiprotein biomarkers in peripheral blood mononuclear cells

Background

Amyotrophic lateral sclerosis (ALS) is a fatal progressive motor neuron disease, for which there are still no diagnostic/prognostic test and therapy. Specific molecular biomarkers are urgently needed to facilitate clinical studies and speed up the development of effective treatments.

Methodology/Principal Findings

We used a two-dimensional difference in gel electrophoresis approach to identify in easily accessible clinical samples, peripheral blood mononuclear cells (PBMC), a panel of protein biomarkers that are closely associated with ALS. Validations and a longitudinal study were performed by immunoassays on a selected number of proteins. The same proteins were also measured in PBMC and spinal cord of a G93A SOD1 transgenic rat model. We identified combinations of protein biomarkers that can distinguish, with high discriminatory power, ALS patients from healthy controls (98%), and from patients with neurological disorders that may resemble ALS (91%), between two levels of disease severity (90%), and a number of translational biomarkers, that link responses between human and animal model. We demonstrated that TDP-43, cyclophilin A and ERp57 associate with disease progression in a longitudinal study. Moreover, the protein profile changes detected in peripheral blood mononuclear cells of ALS patients are suggestive of possible intracellular pathogenic mechanisms such as endoplasmic reticulum stress, nitrative stress, disturbances in redox regulation and RNA processing.

Conclusions/Significance

Our results indicate that PBMC multiprotein biomarkers could contribute to determine amyotrophic lateral sclerosis diagnosis, differential diagnosis, disease severity and progression, and may help to elucidate pathogenic mechanisms.

Alteration of protein folding and degradation in motor neuron diseases: Implications and protective functions of small heat shock proteins

Motor neuron diseases (MNDs) are neurodegenerative disorders that specifically affect the survival and function of upper and/or lower motor neurons. Since motor neurons are responsible for the control of voluntary muscular movement, MNDs are characterized by muscle spasticity, weakness and atrophy. Different susceptibility genes associated with an increased risk to develop MNDs have been reported and several mutated genes have been linked to hereditary forms of MNDs. However, most cases of MNDs occur in sporadic forms and very little is known on their causes. Interestingly, several molecular mechanisms seem to participate in the progression of both the inherited and sporadic forms of MNDs. These include cytoskeleton organization, mitochondrial functions, DNA repair and RNA synthesis/processing, vesicle trafficking, endolysosomal trafficking and fusion, as well as protein folding and protein degradation. In particular, accumulation of aggregate-prone proteins is a hallmark of MNDs, suggesting that the protein quality control system (molecular chaperones and the degradative systems: ubiquitin-proteasome-system and autophagy) are saturated or not sufficient to allow the clearance of these altered proteins. In this review we mainly focus on the MNDs associated with disturbances in protein folding and protein degradation and on the potential implication of a specific class of molecular chaperones, the small heat shock proteins (sHSPs/HSPBs), in motor neuron function and survival. How boosting of specific HSPBs may be a potential useful therapeutic approach in MNDs and how mutations in specific HSPBs can directly cause motor neuron degeneration is discussed.

Impaired motoneuronal retrograde transport in two models of SBMA implicates two sites of androgen action

Spinal and bulbar muscular atrophy (SBMA) impairs motor function in men and is linked to a CAG repeat mutation in the androgen receptor (AR) gene. Defects in motoneuronal retrograde axonal transport may critically mediate motor dysfunction in SBMA, but the site(s) where AR disrupts transport is unknown. We find deficits in retrograde labeling of spinal motoneurons in both a knock-in (KI) and a myogenic transgenic (TG) mouse model of SBMA. Likewise, live imaging of endosomal trafficking in sciatic nerve axons reveals disease-induced deficits in the flux and run length of retrogradely transported endosomes in both KI and TG males, demonstrating that disease triggered in muscle can impair retrograde transport of cargo in motoneuron axons, possibly via defective retrograde signaling. Supporting the idea of impaired retrograde signaling, we find that vascular endothelial growth factor treatment of diseased muscles reverses the transport/trafficking deficit. Transport velocity is also affected in KI males, suggesting a neurogenic component. These results demonstrate that androgens could act via both cell autonomous and non-cell autonomous mechanisms to disrupt axonal transport in motoneurons affected by SBMA.

Motoneuron subtypes show specificity in glycine receptor channel abnormalities in a transgenic mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by selective loss of motoneurons. Recently we studied glycine receptors (GlyRs) in motoneurons in an ALS mouse model expressing a mutant form of human superoxide dismutase-1 with a Gly93→Ala substitution (G93A-SOD1). Living motoneurons in dissociated spinal cord cultures were identified by using transgenic mice expressing eGFP driven by the Hb9 promoter. We showed that GlyR-mediated currents were reduced in large-sized (diameter > 28 μm) Hb9-eGFP(+) motoneurons from G93A-SOD1 embryonic mice. Here we analyze GlyR currents in a morphologically distinct subgroup of medium-sized (diameter 10-28 μm) Hb9-eGFP(+) motoneurons, presumably gamma or slow-type alpha motoneurons. We find that glycine-induced current densities were not altered in medium-sized G93A-SOD1 motoneurons. No significant differences in glycinergic mIPSCs were observed between G93A-SOD1 and control medium-sized motoneurons. These results indicate that GlyR deficiency early in the disease process of ALS is specific for large alpha motoneurons.

Granulocyte colony stimulating factor attenuates inflammation in a mouse model of amyotrophic lateral sclerosis

BACKGROUND

Granulocyte colony stimulating factor (GCSF) is protective in animal models of various neurodegenerative diseases. We investigated whether pegfilgrastim, GCSF with sustained action, is protective in a mouse model of amyotrophic lateral sclerosis (ALS). ALS is a fatal neurodegenerative disease with manifestations of upper and lower motoneuron death and muscle atrophy accompanied by inflammation in the CNS and periphery.

METHODS

Human mutant G93A superoxide dismutase (SOD1) ALS mice were treated with pegfilgrastim starting at the presymptomatic stage and continued until the end stage. After long-term pegfilgrastim treatment, the inflammation status was defined in the spinal cord and peripheral tissues including hematopoietic organs and muscle. The effect of GCSF on spinal cord neuron survival and microglia, bone marrow and spleen monocyte activation was assessed in vitro.

RESULTS

Long-term pegfilgrastim treatment prolonged mutant SOD1 mice survival and attenuated both astro- and microgliosis in the spinal cord. Pegfilgrastim in SOD1 mice modulated the inflammatory cell populations in the bone marrow and spleen and reduced the production of pro-inflammatory cytokine in monocytes and microglia. The mobilization of hematopoietic stem cells into the circulation was restored back to basal level after long-term pegfilgrastim treatment in SOD1 mice while the storage of Ly6C expressing monocytes in the bone marrow and spleen remained elevated. After pegfilgrastim treatment, an increased proportion of these cells in the degenerative muscle was detected at the end stage of ALS.

CONCLUSIONS

GCSF attenuated inflammation in the CNS and the periphery in a mouse model of ALS and thereby delayed the progression of the disease. This mechanism of action targeting inflammation provides a new perspective of the usage of GCSF in the treatment of ALS.

SOD1 and TDP-43 animal models of amyotrophic lateral sclerosis: recent advances in understanding disease toward the development of clinical treatments

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease with no cure. Breakthroughs in understanding ALS pathogenesis came with the discovery of dominant mutations in the superoxide dismutase 1 gene (SOD1) and other genes, including the gene encoding transactivating response element DNA binding protein-43 (TDP-43). This has led to the creation of animal models to further our understanding of the disease and identify a number of ALS-causing mechanisms, including mitochondrial dysfunction, protein misfolding and aggregation, oxidative damage, neuronal excitotoxicity, non-cell autonomous effects and neuroinflammation, axonal transport defects, neurotrophin depletion, effects from extracellular mutant SOD1, and aberrant RNA processing. Here we summarise the SOD1 and TDP-43 animal models created to date, report on recent findings supporting the potential mechanisms of ALS pathogenesis, and correlate this understanding with current developments in the clinic.

Treatment with trichostatin A initiated after disease onset delays disease progression and increases survival in a mouse model of amyotrophic lateral sclerosis

Recent studies suggest that progressive motoneuron death in amyotrophic lateral sclerosis (ALS) is non-cell autonomous and may involve the participation of non-neuronal cells such as glial cells and skeletal muscle. Therefore, a drug that targets motoneurons as well as neighboring non-neuronal cells might be a potential therapeutic strategy to delay disease progression in ALS. Trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, has shown protective effects in multiple cell types implicated in ALS by resetting gene transcription profiles through increased histone acetylation. To test whether TSA could serve as a potential therapeutic agent, we intraperitoneally injected TSA from postnatal day 90 (P90), after disease symptoms appear, until P120 or the end-stage in SOD1-G93A mice. We found that TSA ameliorated motoneuron death and axonal degeneration in SOD1-G93A mice. Reduced gliosis and upregulation of the glutamate transporter (GLT-1) were also observed in the spinal cord of TSA-treated SOD1-G93A mice. In addition, TSA ameliorated muscle atrophy and neuromuscular junction (NMJ) denervation, which are the pathological characteristics of ALS found in skeletal muscle. Improved morphology in TSA-treated SOD1-G93A mice was accompanied by enhanced motor functions as assessed by rota-rod and grip strength analyses. Furthermore, TSA treatment significantly increased the mean survival duration after the treatment by 18% and prolonged lifespan by 7%. Our findings suggest that TSA may provide a potential therapy to slow disease progression as well as to enhance motor performance to improve the quality of life for ALS patients.

Motor neuron trophic factors: therapeutic use in ALS?

The modest effects of neurotrophic factor (NTF) treatment on lifespan in both animal models and clinical studies of Amyotropic Lateral Sclerosis (ALS) may result from any one or combination of the four following explanations: 1.) NTFs block cell death in some physiological contexts but not in ALS; 2.) NTFs do not rescue motoneurons (MNs) from death in any physiological context; 3.) NTFs block cell death in ALS but to no avail; and 4.) NTFs are physiologically effective but limited by pharmacokinetic constraints. The object of this review is to critically evaluate the role of both NTFs and the intracellular cell death pathway itself in regulating the survival of spinal and cranial (lower) MNs during development, after injury and in response to disease. Because the role of molecules mediating MN survival has been most clearly resolved by the in vivo analysis of genetically engineered mice, this review will focus on studies of such mice expressing reporter, null or other mutant alleles of NTFs, NTF receptors, cell death or ALS-associated genes.

ALS: focus on purinergic signalling

Amyotrophic lateral sclerosis (ALS) is one of the most common neuromuscular diseases. It is devastating and fatal, causing progressive paralysis of all voluntary muscles and eventually death, while sparing cognitive functions. A pathological hallmark of ALS is neuroinflammation mediated by non-neuronal cells in the nervous system, such as microglia and astrocytes that accelerate the disease progression. Scientists have neither found a unique key mechanism, nor an effective treatment against ALS, supposedly because it is a multi-factorial and multi-systemic disease. Extracellular purines and pyrimidines are widespread and powerful physiopathological molecules, signalling to most cell types and directing cell-to-cell communication networks. They are instrumental for instance for neurotransmission, muscle contraction and immune surveillance. Recent work has reported the crucial involvement of purinergic pathways in many neurodegenerative and neuroinflammatory diseases, comprising ALS. Especially P2 receptors for ATP, P1 receptors for adenosine, and nucleotide transporters were found to be modulated in ALS cells and tissues, playing a potential role in the disease. Given the composite cellular cross-talk occurring during ALS and the established action of extracellular purines/pyrimidines as neuron-to-glia alarm signal in the nervous system, a mutual query in these two fields should now be whether, how and when purinergic would meet ALS. In this review, we will highlight the early cellular and molecular purinergic cross-talk that participates to ALS etiopathology, with the conviction that better understanding of purinergic dynamics might provide original research perspectives, stimulate alternative disease modelling, and the design and testing of more powerful targeted therapeutics against this relentlessly progressive disorder.

Muscle cells and motoneurons differentially remove mutant SOD1 causing familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motoneuronal disease which occurs in sporadic or familial forms, clinically indistinguishable. About 15% of familial ALS cases are linked to mutations of the superoxide dismutase 1 (SOD1) gene that may induce misfolding in the coded protein, exerting neurotoxicity to motoneurons. However, other cell types might be target of SOD1 toxicity, because muscle-restricted expression of mutant SOD1 correlates with muscle atrophy and motoneurons death. We analysed the molecular behaviour of mutant SOD1 in motoneuronal NSC34 and muscle C2C12 cells. We found that misfolded mutant SOD1 clearance is much more efficient in muscle C2C12 than in motoneuronal NSC34 cells. Mutant SOD1 forms aggregates and impairs the proteasome only in motoneuronal NSC34 cells. Interestingly, NSC34 cells expressing mutant SOD1 are more sensitive to a superoxide-induced oxidative stress. Moreover, in muscle C2C12 cells mutant SOD1 remains soluble even when proteasome is inhibited with MG132. The higher mutant SOD1 clearance in muscle cells correlates with a more efficient proteasome activity, combined with a robust autophagy activation. Therefore, muscle cells seem to better manage misfolded SOD1 species, not because of an intrinsic property of the mutant protein, but in function of the cell environment, indicating also that the SOD1 toxicity at muscle level may not directly depend on its aggregation rate.

Mitochondria as a therapeutic target for aging and neurodegenerative diseases

Mitochondria are cytoplasmic organelles responsible for life and death. Extensive evidence from animal models, postmortem brain studies of and clinical studies of aging and neurodegenerative diseases suggests that mitochondrial function is defective in aging and neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Several lines of research suggest that mitochondrial abnormalities, including defects in oxidative phosphorylation, increased accumulation of mitochondrial DNA defects, impaired calcium influx, accumulation of mutant proteins in mitochondria, and mitochondrial membrane potential dissipation are important cellular changes in both early and late-onset neurodegenerative diseases. Further, emerging evidence suggests that structural changes in mitochondria, including increased mitochondrial fragmentation and decreased mitochondrial fusion, are critical factors associated with mitochondrial dysfunction and cell death in aging and neurodegenerative diseases. This paper discusses research that elucidates features of mitochondria that are associated with cellular dysfunction in aging and neurodegenerative diseases and discusses mitochondrial structural and functional changes, and abnormal mitochondrial dynamics in neurodegenerative diseases. It also outlines mitochondria-targeted therapeutics in neurodegenerative diseases.

Hind limb muscle atrophy precedes cerebral neuronal degeneration in G93A-SOD1 mouse model of amyotrophic lateral sclerosis: a longitudinal MRI study

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal, neurodegenerative disorder caused by the degeneration of motor neurons in the CNS, which results in complete paralysis of skeletal muscles. Recent experimental studies have suggested that the disease could initiate in skeletal muscle, rather than in the motor neurons. To establish the timeframe of motor neuron degeneration in relation to muscle atrophy in motor neuron disease, we have used MRI to monitor changes throughout disease in brain and skeletal muscle of G93A-SOD1 mice, a purported model of ALS. Longitudinal MRI examination of the same animals indicated that muscle volume in the G93A-SOD1 mice was significantly reduced from as early as week 8 of life, 4 weeks prior to clinical onset. Progressive muscle atrophy from week 8 onwards was confirmed by histological analysis. In contrast, brain MRI indicated that neurodegeneration occurs later in G93A-SOD1 mice, with hyperintensity MRI signals detected only at weeks 10-18. Neurodegenerative changes were observed only in the motor nuclei areas of the brainstem; MRI changes indicative of neurodegeneration were not detected in the motor cortex where first motor neurons originate, even at the late disease stage. This longitudinal MRI study establishes unequivocally that, in the experimental murine model of ALS, muscle degeneration occurs before any evidence of neurodegeneration and clinical signs, supporting the postulate that motor neuron disease can initiate from muscle damage and result from retrograde dying-back of the motor neurons.

Abnormalities of satellite cells function in amyotrophic lateral sclerosis

Abstract Amyotrophic lateral sclerosis (ALS) is characterized by progressive denervation leading to muscle atrophy prevented, during the early phase, by compensatory reinnervation. Little is known about muscle fibre regeneration capacity in ALS. We have carried out in vivo and in vitro investigation of skeletal muscle in ALS. Seven ALS patients underwent a deltoid muscle biopsy. Immunohistochemical analysis revealed various degrees of denervation- and reinnervation-related changes in the ALS muscle biopsies including satellite cells (SCs) activation and regenerating fibres. Only 3/7 primary cultures of ALS muscle cells were successfully established and had sufficient myogenicity, as assessed by desmin positivity, to be used without further purification. This was in contrast with the cultures derived from control muscles, predominantly desmin-positive cells. Although capable to proliferate in vitro, ALS-derived SCs presented an abnormal senescent-like morphology. Markers of senescence, including senescent-associated (SA)-βGal activity and p16 expression, were increased. Furthermore, ALS-derived SCs were also unable to fully differentiate in vitro as shown by abnormal myotubes morphology and reduced MHC isoform expression, compared to control myotubes. Our study suggests that SC function is altered in ALS. This could limit the efficacy of compensatory processes and therefore could contribute to the progression of muscle atrophy and weakness.

Muscle atrophy induced by SOD1G93A expression does not involve the activation of caspase in the absence of denervation

Background

The most remarkable feature of skeletal muscle is the capacity to adapt its morphological, biochemical and molecular properties in response to several factors. Nonetheless, under pathological conditions, skeletal muscle loses its adaptability, leading to atrophy or wasting. Several signals might function as physiopathological triggers of muscle atrophy. However, the specific mechanisms underlying the atrophic phenotype under different pathological conditions remain to be fully elucidated. In this paper, we address the involvement of caspases in the induction of muscle atrophy in experimental models of amyotrophic lateral sclerosis (ALS) expressing the mutant SOD1^G93A transgene either locally or ubiquitously.

Results

We demonstrate that SOD1^G93A-mediated muscle atrophy is independent from caspase activity. In particular, the expression of SOD1^G93A promotes a reduction of the phosphatidylinositol 3-kinase/Akt pathway associated with activation of forkhead box O3. In contrast, the activation of caspases occurs later and is causally linked to motor neuron degeneration, which is associated with exacerbation of the atrophic phenotype and a shift in fiber-type composition.

Conclusion

This study suggests that muscle atrophy induced by the toxic effect of SOD1^G93A is independent from the activation of apoptotic markers and that caspase-mediated apoptosis is a process activated upon muscle denervation.

Genetic rodent models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the selective death of motor neurons in the motor cortex, brainstem, and spinal cord. A large number of rodent models are available that show motor neuron death and a progressive motor phenotype that is more or less reminiscent of what occurs in patients. These rodent models contain genes with spontaneous or induced mutations or (over) express different (mutant) genes. Some of these models have been of great value to delineate potential pathogenic mechanisms that cause and/or modulate selective motor neuron degeneration. In addition, these genetic rodent models play a crucial role in testing and selecting potential therapeutics that can be used to treat ALS and/or other motor neuron disorders. In this paper, we give a systematic overview of the most important genetic rodent models that show motor neuron degeneration and/or develop a motor phenotype. In addition, we discuss the value and limitations of the different models and conclude that it remains a challenge to find more and better rodent models based on mutations in new genes causing ALS.

Skeletal muscle in motor neuron diseases: therapeutic target and delivery route for potential treatments

Lower motor neuron (LMN) degeneration occurs in several diseases that affect patients from neonates to elderly and can either be genetically transmitted or occur sporadically. Among diseases involving LMN degeneration, spinal muscular atrophy (SMA) and spinal bulbar muscular atrophy (Kennedy's disease, SBMA) are pure genetic diseases linked to loss of the SMN gene (SMA) or expansion of a polyglutamine tract in the androgen receptor gene (SBMA) while amyotrophic lateral sclerosis (ALS) can either be of genetic origin or occur sporadically. In this review, our aim is to put forward the hypothesis that muscle fiber atrophy and weakness might not be a simple collateral damage of LMN degeneration, but instead that muscle fibers may be the site of crucial pathogenic events in these diseases. In SMA, the SMN gene was shown to be required for muscle structure and strength as well as for neuromuscular junction formation, and a subset of SMA patients develop myopathic pathology. In SBMA, the occurrence of myopathic histopathology in patients and animal models, along with neuromuscular phenotype of animal models expressing the androgen receptor in muscle only has lead to the proposal that SBMA may indeed be a muscle disease. Lastly, in ALS, at least part of the phenotype might be explained by pathogenic events occuring in skeletal muscle. Apart from its potential pathogenic role, skeletal muscle pathophysiological events might be a target for treatments and/or be a preferential route for targeting motor neurons.

State of the art and the dark side of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a disorder that involves the degeneration of motor neurons, muscle atrophy, and paralysis. In a few familiar forms of ALS, mutations in the superoxide dismutase-1 (SOD1) gene have been held responsible for the degeneration of motor neurons. Nevertheless, after the discovery of the SOD1 mutations no consensus has emerged as to which cells, tissues and pathways are primarily implicated in the pathogenic events that lead to ALS. Ubiquitous overexpression of mutant SOD1 in transgenic animals recapitulates the pathological features of ALS. However, the toxicity of mutant SOD1 is not necessarily limited to the central nervous system. Views about ALS pathogenesis are now enriched by the recent discovery of mutations in a pair of DNA/RNA-binding proteins called TDP-43 and FUS/TLS as causes of familial and sporadic forms of ALS. Although the steps that lead to the pathological state are well defined, several fundamental issues are still controversial: are the motor neurons the first direct targets of ALS; and what is the contribution of non-neuronal cells, if any, to the pathogenesis of ALS? The state of the art of ALS pathogenesis and the open questions are discussed in this review.