Involvement of sensory innervation in the skin of SOD1G93A ALS mice

Sensory alterations have been described in both amyotrophic lateral sclerosis (ALS) patients and mouse models. While involvement of intraepidermal and subepidermal axons has been shown in skin biopsies of ALS patients, it is unclear if the SOD1^G93A mouse presents similar alterations. We analyzed the epidermal and dermal innervation, based on PGP9.5 immunostaining, of SOD1^G93A mice at different stages. The results showed a marked reduction of intraepidermal nerve fibers, Meissner's corpuscles, and subepidermal nerve density already at 4 weeks. This loss of innervation progressed over time. Dermal axonal density decreased at a later stage of the disease. There was a gradient of axonal loss, with a more severe decline in the epidermis compared with deeper structures, indicating a distal axonal neuropathy as the mechanism of degeneration. These findings suggest that the analysis of the cutaneous sensory innervation may be an accessible and useful tool to assess the neurodegeneration process in motoneuron diseases.     

Contractile characteristics of gastrocnemius-soleus muscle in the SOD1G93A ALS mouse model

Abstract

Objectives:

In the SOD1G93A mouse model of amyotrophic lateral sclerosis (ALS), a selective degeneration of fast-fatigable motor units and consequently an early decline of contractile force in individual fast-twitch muscles have been observed in the preclinical stage. However, most human muscles include fast and slow motor units. Gastrocnemius-soleus group (GS) contains such a mixture of units.

Methods:

We have investigated changes in the mechanical properties of GS at different SOD1G93A stages in mice. For this purpose, the tibial nerve was repetitively stimulated with rectangular pulses and the force of GS twitches was recorded using a strain gauge fixed to the Achilles tendon.

Results:

Isometric and tetanic force were attenuated but not before the first clinical signs developed. However, already at preclinical stages, single twitches showed a slower decay compared to control. Consequently, fusion of GS twitches occurred at lower stimulus rates. Furthermore, already preclinically, the temporal course of successive twitch amplitudes changed during repetitive stimulation at increasing rates. The peak amplitudes as well as the potentiation following decay (fatigue) were lower in preclinical mice than in control.

Discussion:

The time-lapse analysis of the contractile pattern as well as of the twitch configuration of the mixed muscle GS have revealed distinctive differences between wild-type controls and preclinical SOD1G93A mice. It would be of interest to know whether these preclinical changes are also detectable in ALS patients.     

Effects of intraperitoneal injection of Rofecoxib in a mouse model of ALS

There is increasing evidence that inflammatory mechanisms are involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). Inhibition of a key mediator of inflammation, cyclooxygenase 2 (COX-2), represents a promising therapeutic approach in ALS. Here we tested the in vivo effects of a specific COX-2 inhibitor, Rofecoxib, administered by intraperitoneal injection, in the SOD1(G93A G1H) mouse model of the familial form of ALS (fALS). Rofecoxib administration commenced at postnatal day 60 (P60), since the hallmarks of inflammation in the spinal cord were found to occur beyond this time-point in this mouse model of fALS. We found a significant but small delay in the onset of locomotor impairment in mice treated with Rofecoxib at the dose of 10 mg/kg of weight. However, survival was not effected by treatment. As prostaglandin E2 levels in spinal cord or in plasma were not reduced by Rofecoxib treatment, these results may suggest lack of sufficient bioavailability as the reason for the modest clinical changes observed.     

Novel SOD1 N86K mutation is associated with a severe phenotype in familial ALS

Familial amyotrophic lateral sclerosis (ALS) is frequently associated with mutations in the SOD1 gene. We identified a rapidly progressive disease in a patient with an inherited ALS. The identified heterozygous T>A exchange in position 1067 in the SOD1 gene results in an amino acid substitution of lysine for asparagine at position 86 (N86K) of the SOD1 protein. The family history suggested that this autosomal dominantly inherited mutation may be associated with rapidly progressive disease.     

Rasagiline alone and in combination with riluzole prolongs survival in an ALS mouse model

Abstract. Rasagiline is an antiapoptotic compound with neuroprotective potential. We examined its neuroprotective effect alone and in combination with the putative glutamate release blocker riluzole in the G93A model of familial amyotrophic lateral sclerosis (fALS). Endpoints of experimental treatment were survival and motor activity. The drug had a significant dose-dependent therapeutic effect on both preclinical and clinical motor function and survival of the animals. We also found that the combination of rasagiline with riluzole is safe and increases survival by about 20 % in a dosedependent manner. Therefore, we conclude that the combination of rasagiline and riluzole is a promising clinical combination for the improvement of current neuroprotective treatment strategies of ALS.     

Glutamate AMPA receptors change in motor neurons of SOD1G93A transgenic mice and their inhibition by a noncompetitive antagonist ameliorates the progression of amytrophic lateral sclerosis-like disease

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder involving the selective degeneration of motor neurons. In a small proportion of patients, ALS is caused by mutations in copper/zinc superoxide dismutase (SOD1), and mice overexpressing SOD1(G93A) mutant develop a syndrome that closely resembles the human disease. Excitotoxicity mediated by glutamate AMPA receptors has been suggested to be implicated in the selective susceptibility of motor neurons occurring in ALS. In SOD1(G93A) mice, we found that levels of GluR2 AMPA subunit, which plays a pivotal role in the maintenance of calcium impermeability of AMPA receptors, are decreased in spinal motor neurons before symptom onset in concomitance with a modest increase of GluR3 expression, a calcium-permeable AMPA subunit. This effect can result in a higher number of calcium-permeable AMPA receptors on motor neurons of SOD1(G93A) mice, predisposing these cells to be injured by AMPA-mediated glutamate firing. In support of this, we showed that treatment with a new noncompetitive AMPA antagonist, ZK 187638, partially protected motor neurons, improved motor function, and prolonged the survival of SOD1(G93A) mice.     

Presymptomatic electrophysiological tests predict clinical onset and survival in SOD1G93A ALS mice

Introduction: We assessed the predictive value of electrophysiological tests as a marker of clinical disease onset and survival in superoxide‐dismutase 1 (SOD1)^G93A mice. Methods: We evaluated the accuracy of electrophysiological tests in differentiating transgenic versus wild‐type mice. We made a correlation analysis of electrophysiological parameters and the onset of symptoms, survival, and number of spinal motoneurons. Results: Presymptomatic electrophysiological tests show great accuracy in differentiating transgenic versus wild‐type mice, with the most sensitive parameter being the tibialis anterior compound muscle action potential (CMAP) amplitude. The CMAP amplitude at age 10 weeks correlated significantly with clinical disease onset and survival. Electrophysiological tests increased their survival prediction accuracy when evaluated at later stages of the disease and also predicted the amount of lumbar spinal motoneuron preservation. Conclusions: Electrophysiological tests predict clinical disease onset, survival, and spinal motoneuron preservation in SOD1^G93A mice. This is a methodological improvement for preclinical studies. Muscle Nerve 50: 943–949, 2014     

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

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

Interferon‐γ Receptor 1 and GluR1 upregulated in motor neurons of symptomatic hSOD1G93A mice

Motor neurons are markedly vulnerable to excitotoxicity mostly by alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic receptor (AMPAR) stimulation and are principal targets in the neurodegenerative disease Amyotrophic Lateral Sclerosis. Interferon‐gamma (IFN‐γ), a pro‐inflammatory cytokine, can independently cause neuronal dysfunction by triggering calcium influx through a calcium‐permeable complex of IFN‐γ receptor 1(IFNGR1) subunit and AMPAR subunit GluR1. This receptor complex is formed via a non‐canonical neuron‐specific IFN‐γ pathway that involves Jak1/Stat1 and Protein Kinase A. In this study, we explore the expression of the pathway's participants for the first time in the hSOD1G93A Amyotrophic Lateral Sclerosis mouse model. Elevated IFNGR1 and GluR1 are detected in motor neurons of hSOD1G93A symptomatic mice ex vivo, unlike the downstream targets ‐ Jak1, Stat1, and Protein Kinase A. We, also, determine effects of IFN‐γ alone or in the presence of an excitotoxic agent, kainate, on motor neuron survival in vitro. IFN‐γ induces neuronal damage, but does not influence kainate‐mediated excitotoxicity. Increased IFNGR1 can most likely sensitize motor neurons to excitotoxic insults involving GluR1 and/or pathways mediated by IFN‐γ, thus, serving as a potential direct link between neurodegeneration and inflammation in Amyotrophic Lateral Sclerosis.     

Exon 5 encoded domain is not required for the toxic function of mutant SOD1 but essential for the dismutase activity: identification and characterization of two new SOD1 mutations associated with familial amyotrophic lateral sclerosis

Two new mutations in the gene encoding cytoplasmic Cu,Zn superoxide dismutase (SOD1) have been discovered in patients with familial amyotrophic lateral sclerosis (FALS). These mutations result in the truncation of most of the polypeptide segment encoded by exon 5, one by the formation of a stop codon in codon 126 (L126Z) and the other by inducing alternative splicing in the mRNA (splicing junction mutation). These two mutants of SOD1 result in a FALS phenotype similar to that observed in patients with missense mutations in the SOD1 gene, establishing that exon 5 is not required for the novel toxic functions of mutant SOD1 associated with ALS. These mutant enzymes are present at very low levels in FALS patients, suggesting elevated toxicity compared to mutant enzymes with single site substitutions. This increased toxicity likely arises from the extreme structural and functional changes in the active site channel, β-barrel fold, and dimer interface observed in the mutant enzymes, including the loss of native dismutase activity. In particular, the truncation of the polypeptide chain dramatically opens the active site channel, resulting in a marked increase in the accessibility and flexibility of the metal ions and side chain ligands of the enzyme active site. These structural changes are proposed to cause a decrease in substrate specificity and an increase in the catalysis of harmful chemical reactions such as peroxidation. Received February 17, 1997; Revised and Accepted March 5, 1997     

Involvement of CHOP, an ER-stress apoptotic mediator, in both human sporadic ALS and ALS model mice

Endoplasmic reticulum (ER) stress-induced neuronal death may play a critical role in the pathogenesis of amyotrophic lateral sclerosis (ALS). However, whether CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP), an ER-stress apoptotic mediator, is involved in the pathogenesis of ALS is controversial. Here we demonstrate the expression levels and localization of CHOP in spinal cords of both sporadic ALS patients and ALS transgenic mice by immunohistochemistry. In the spinal cords of sporadic ALS patients, CHOP was markedly up-regulated but typically expressed at low levels in those of the control. Likewise, CHOP expression increased at 14 (symptomatic stage) and 18 to 20  weeks (end stage) in ALS transgenic mice spinal cords. Furthermore, localizations of CHOP were merged in motor neurons and glial cells, such as oligodendrocytes, astrocytes, and microglia. These results indicate that the up-regulation of CHOP in motor neurons and glial cells may play pivotal roles in the pathogenesis of ALS.     

Limited effects of glatiramer acetate in the high-copy number hSOD1-G93A mouse model of ALS

In amyotrophic lateral sclerosis (ALS), an involvement of the immune system in the degenerative processes has been shown in both humans and the transgenic SOD1-G93A mice. We previously showed that Glatiramer acetate (also known as copolymer-1; COP-1; Copaxone) improves motor function and extends survival times in an inbred strain of ALS mice probably by interacting with pro-inflammatory T(H) lymphocytes. In the course of this study we tested whether these beneficial effects could be reproduced by repeated vaccination of animals with COP-1 without co-administration of complete Freund's adjuvant. In an outbred strain we could not demonstrate a positive effect of COP-1 on survival times, but found a significant improvement of motor performance during the late stage of disease and a moderate decrease of the production of the inflammatory cytokines interferon-gamma and IL-4 by T lymphocytes isolated from the mice's spleen. In conclusion, the effects of COP-1 in the applied hybrid strain displaying a faster disease progression were less pronounced than in the earlier tested inbred strain of ALS mice.     

Altered immunoreactivity of ErbB4, a causative gene product for ALS19, in the spinal cord of patients with sporadic ALS

ErbB4 is the protein implicated in familial amyotrophic lateral sclerosis (ALS), designated as ALS19. ErbB4 is a receptor tyrosine kinase activated by its ligands, neuregulins (NRG), and plays an essential role in the function and viability of motor neurons. Mutations in the ALS19 gene lead to the reduced autophosphorylation capacity of the ErbB4 protein upon stimulation with NRG‐1, suggesting that the disruption of the NRG–ErbB4 pathway causes motor neuron degeneration. We used immunohistochemistry to study ErbB4 in the spinal cord of patients with sporadic ALS (SALS) to test the hypothesis that ErbB4 may be involved in the pathogenesis of SALS. ErbB4 was specifically immunoreactive in the cytoplasm of motor neurons in the anterior horns of the spinal cord. In patients with SALS, some of the motor neurons lost immunoreactivity with ErbB4, with the proportion of motor neurons with a loss of immunoreactivity correlated with the severity of motor neuron loss. The subcellular localization was altered, demonstrating nucleolar or nuclear localization, threads/dots and spheroids. The ectopic glial immunoreactivity was observed, mainly in the oligodendrocytes of the lateral columns and anterior horns. The reduction in the ErbB4 immunoreactivity was significantly correlated with the cytoplasmic mislocalization of transactivation response DNA‐binding protein 43 kDa (TDP‐43) in the motor neurons. No alteration in immunoreactivity was observed in the motor neurons of mice carrying atransgene for mutant form of the superoxide dismutase 1 gene (SOD1). This study provided compelling evidence that ErbB4 is also involved in the pathophysiology of SALS, and that the disruption of the NRG–ErbB4 pathway may underlie the TDP‐43‐dependent motor neuron degeneration in ALS.     

Elevated levels of amyloid precursor protein in muscle of patients with amyotrophic lateral sclerosis and a mouse model of the disease

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease defined by motor neuron loss. Transgenic mouse models show features that closely mimic those seen in the clinical situation, reflected in the molecular changes observed in mouse models and in tissues from patients. We report a dramatic increase in the expression of amyloid precursor protein (APP) in the hindlimb muscles, but not the spinal cord of the G93A transgenic mouse model, significantly before the appearance of clinical abnormalities. APP levels were unchanged in nontransgenic mice and in mice overexpressing human wild-type Cu/Zn-dependent superoxide dismutase 1 (SOD1). Preliminary results indicate a similar change in APP expression in human deltoid muscle samples from ALS patients compared with age-matched controls. The inhibitory role of APP in innervation at the neuromuscular junction and increased expression in inclusion-body myositis suggest that presymptomatic upregulation of APP may be consistent with a potential role for APP in ALS pathology.     

Relationship between neuropathology and disease progression in the SOD1(G93A) ALS mouse

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of upper and lower motor neurons. However, recent reports suggest an active role of non-neuronal cells in the pathogenesis of the disease. Here, we examined quantitatively the temporal development of neuropathologic features in the brain and spinal cord of a mouse model of ALS (SOD1^G93A). Four phases of the disease were studied in both male and female SOD1^G93A mice: presymptomatic (PRE-SYM), symptomatic (SYM), endstage (ES) and moribund (MB). Compared to their control littermates, SOD1^G93A mice showed an increase in astrogliosis in the motor cortex, spinal cord and motor trigeminal nucleus in the SYM phase that worsened progressively in ES and MB animals. Associated with this increase in astrogliosis was a concomitant increase in motor neuron cell death in the spinal cord and motor trigeminal nucleus in both ES and MB mice, as well as in the ventrolateral thalamus in MB animals. In contrast, microglial activation was significantly increased in all the same regions but only when the mice were in the MB phase. These results suggest that astrogliosis preceded or occurred concurrently with neuronal degeneration whereas prominent microgliosis was evident later (MB stage), after significant motor neuron degeneration had occurred. Hence, our findings support a role for astrocytes in modulating the progression of non-cell autonomous degeneration of motor neurons, with microglia playing a role in clearing degenerating neurons.