Cu/Zn-superoxide dismutase (GLY93→ALA) mutation alters AMPA receptor subunit expression and function and potentiates kainate-mediated toxicity in motor neurons in culture

GluA3-containing AMPA receptors: From physiology to synaptic dysfunction in brain disorders

In the mammalian brain, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) play a fundamental role in the activation of excitatory synaptic transmission and the induction of different forms of synaptic plasticity. The modulation of the AMPAR tetramer subunit composition at synapses defines the functional properties of the receptor. During the last twenty years, several studies have evaluated the roles played by each subunit, from GluA1 to GluA4, in both physiological and pathological conditions. Here, we have focused our attention on GluA3-containing AMPARs, addressing their functional role in synaptic transmission and synaptic plasticity and their involvement in a variety of brain disorders. Although several aspects remain to be fully understood, GluA3 is a widely expressed and functionally relevant subunit in AMPARs involved in several brain circuits, and its pharmacological modulation could represent a novel approach for the rescue of altered glutamatergic synapses associated with neurodegenerative and neurodevelopmental disorders.

NeuriTES. Monitoring neurite changes through transfer entropy and semantic segmentation in bright-field time-lapse microscopy

One of the most challenging frontiers in biological systems understanding is fluorescent label-free imaging. We present here the NeuriTES platform that revisits the standard paradigms of video analysis to detect unlabeled objects and adapt to the dynamic evolution of the phenomenon under observation. Object segmentation is reformulated using robust algorithms to assure regular cell detection and transfer entropy measures are used to study the inter-relationship among the parameters related to the evolving system. We applied the NeuriTES platform to the automatic analysis of neurites degeneration in presence of amyotrophic lateral sclerosis (ALS) and to the study of the effects of a chemotherapy drug on living prostate cancer cells (PC3) cultures. Control cells have been considered in both the two cases study. Accuracy values of 93% and of 92% are achieved, respectively. NeuriTES not only represents a tool for investigation in fluorescent label-free images but demonstrates to be adaptable to individual needs.

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Monitoring of cell phenotype changes by fluorescence label-free time-lapse microscopy

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Adaptive semantic segmentation for the robust detection of cell shape

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TE to correlate morphological and textural soma descriptors along time

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Directed TE graph for the representation of mutual relationship among descriptors

One of the most challenging frontiers for the automatic understanding of biological systems is fluorescent label-free imaging in which the behavior changes of living being are characterized without cell staining. To this aim, we present here the NeuriTES platform that revisits standard paradigms of video analysis to detect unlabeled objects and correlate the analysis to phenotype evolution of the mechanisms under observation. Through the exploitation of adaptive algorithms and of transfer entropy measures, the platform assures regular cell detection and the possibility to extract reliable parameters related to the evolving cell system. As a proof-of-concept, NeuriTES is applied to two fascinating phenotype investigation scenarios, amyotrophic lateral sclerosis (ALS) disease mechanism and the study of the effects of a chemotherapy drug on living prostate cancer cells (PC3) cultures. Directed graphs assist the biologists with a visual understanding of the mechanisms identified.

Cerebrospinal fluid from frontotemporal dementia patients is toxic to neurons

Frontotemporal Lobar Degeneration (FTD) is a neurodegenerative disease characterized by a progressive deterioration of cognitive functions. Currently, no effective treatment exists. We have studied cytotoxicity and neuronal functionality in cortical and spinal cord cultures upon exposure to cerebrospinal fluid (CSF) from 39 FTD patients. FTD-CSF alters the miniature excitatory postsynaptic currents in the cortical cultures and it is toxic to spinal cord cultures, particularly to GABAergic+ and calbindin-D28k + neurons.

In vivo brain imaging of mitochondrial Ca2+ in neurodegenerative diseases with multiphoton microscopy

Mitochondria are involved in a large number of essential roles related to neuronal function. Ca²⁺ handling by mitochondria is critical for many of these functions, including energy production and cellular fate. Conversely, mitochondrial Ca²⁺ mishandling has been related to a variety of neurodegenerative diseases. Investigating mitochondrial Ca²⁺ dynamics is essential for advancing our understanding of the role of intracellular mitochondrial Ca²⁺ signals in physiology and pathology. Improved Ca²⁺ indicators, and the ability to target them to different cells and compartments, have emerged as useful tools for analysis of Ca²⁺ signals in living organisms. Combined with state-of-the-art techniques such as multiphoton microscopy, they allow for the study of mitochondrial Ca²⁺ dynamics in vivo in mouse models of the disease. Here, we provide an overview of the Ca²⁺ transporters/ion channels in mitochondrial membranes, and the involvement of mitochondrial Ca²⁺ in neurodegenerative diseases followed by a summary of the main tools available to evaluate mitochondrial Ca²⁺ dynamics in vivo using the aforementioned technique.

Histaminergic transmission slows progression of amyotrophic lateral sclerosis

BACKGROUND

Histamine is an immune modulator, neuroprotective, and remyelinating agent, beneficially acting on skeletal muscles and promoting anti-inflammatory features in amyotrophic lateral sclerosis (ALS) microglia. Drugs potentiating the endogenous release of histamine are in trial for neurological diseases, with a role not systematically investigated in ALS. Here, we examine histamine pathway associations in ALS patients and the efficacy of a histamine-mediated therapeutic strategy in ALS mice.

METHODS

We adopted an integrative multi-omics approach combining gene expression profiles, copy number variants, and single nucleotide polymorphisms of ALS patients. We treated superoxide dismutase 1 (SOD1)-G93A mice that recapitulate key ALS features, with the brain-permeable histamine precursor histidine in the symptomatic phase of the disease and analysed the rescue from disease pathological signs. We examined the action of histamine in cultured SOD1-G93A motor neuron-like cells.

RESULTS

We identified 13 histamine-related genes deregulated in the spinal cord of two ALS patient subgroups, among which genes involved in histamine metabolism, receptors, transport, and secretion. Some histamine-related genes overlapped with genomic regions disrupted by DNA copy number and with ALS-linked pathogenic variants. Histidine treatment in SOD1-G93A mice proved broad efficacy in ameliorating ALS features, among which most importantly lifespan, motor performance, microgliosis, muscle atrophy, and motor neurons survival in vivo and in vitro.

CONCLUSIONS

Our gene set/pathway enrichment analyses and preclinical studies started at the onset of symptoms establish that histamine-related genes are modifiers in ALS, supporting their role as candidate biomarkers and therapeutic targets. We disclose a novel important role for histamine in the characterization of the multi-gene network responsible for ALS and, furthermore, in the drug development process.

Impact of Pharmacological Inhibition of Hydrogen Sulphide Production in the SOD1G93A-ALS Mouse Model

A number of factors can trigger amyotrophic lateral sclerosis (ALS), although its precise pathogenesis is still uncertain. In a previous study done by us, poisonous liquoral levels of hydrogen sulphide (H₂S) in sporadic ALS patients were reported. In the same study very high concentrations of H₂S in the cerebral tissues of the familial ALS (fALS) model of the SOD1G93A mouse, were measured. The objective of this study was to test whether decreasing the levels of H₂S in the fALS mouse could be beneficial. Amino-oxyacetic acid (AOA)—a systemic dual inhibitor of cystathionine-β-synthase and cystathionine-γ lyase (two key enzymes in the production of H₂S)—was administered to fALS mice. AOA treatment decreased the content of H₂S in the cerebral tissues, and the lifespan of female mice increased by approximately ten days, while disease progression in male mice was not affected. The histological evaluation of the spinal cord of the females revealed a significant increase in GFAP positivity and a significant decrease in IBA1 positivity. In conclusion, the results of the study indicate that, in the animal model, the inhibition of H₂S production is more effective in females. The findings reinforce the need to adequately consider sex as a relevant factor in ALS.

Proteomics and Toxicity Analysis of Spinal-Cord Primary Cultures upon Hydrogen Sulfide Treatment

Hydrogen sulfide (H₂S) is an endogenous gasotransmitter recognized as an essential body product with a dual, biphasic action. It can function as an antioxidant and a cytoprotective, but also as a poison with a high probability of causing brain damage when present at noxious levels. In a previous study, we measured toxic liquoral levels of H₂S in sporadic amyotrophic lateral sclerosis (ALS) patients and in the familial ALS (fALS) mouse model, SOD1G93A. In addition, we experimentally demonstrated that H₂S is extremely and selectively toxic to motor neurons, and that it is released by glial cells and increases Ca²⁺ concentration in motor neurons due to a lack of ATP. The presented study further examines the effect of toxic concentrations of H₂S on embryonic mouse spinal-cord cultures. We performed a proteomic analysis that revealed a significant H₂S-mediated activation of pathways related to oxidative stress and cell death, particularly the Nrf-2-mediated oxidative stress response and peroxiredoxins. Furthermore, we report that Na₂S (a stable precursor of H₂S) toxicity is, at least in part, reverted by the Bax inhibitor V5 and by necrostatin, a potent necroptosis inhibitor.

In-vivo effects of knocking-down metabotropic glutamate receptor 5 in the SOD1G93A mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder due to loss of upper and lower motor neurons (MNs). The mechanisms of neuronal death are largely unknown, thus prejudicing the successful pharmacological treatment. One major cause for MN degeneration in ALS is represented by glutamate(Glu)-mediated excitotoxicity. We have previously reported that activation of Group I metabotropic Glu receptors (mGluR1 and mGluR5) at glutamatergic spinal cord nerve terminals produces abnormal Glu release in the widely studied SOD1^G93A mouse model of ALS. We also demonstrated that halving mGluR1 expression in the SOD1^G93A mouse had a positive impact on survival, disease onset, disease progression, and on a number of cellular and biochemical readouts of ALS. We generated here SOD1^G93A mice with reduced expression of mGluR5 (SOD1^G93AGrm5^-/+) by crossing the SOD1^G93A mutant mouse with the mGluR5 heterozigous Grm5^-/+ mouse. SOD1^G93AGrm5^-/+ mice showed prolonged survival probability and delayed pathology onset. These effects were associated to enhanced number of preserved MNs, decreased astrocyte and microglia activation, reduced cytosolic free Ca²⁺ concentration, and regularization of abnormal Glu release in the spinal cord of SOD1^G93AGrm5^-/+ mice. Unexpectedly, only male SOD1^G93AGrm5^-/+ mice showed improved motor skills during disease progression vs. SOD1^G93A mice, while SOD1^G93AGrm5^-/+ females did not. These results demonstrate that a lower constitutive level of mGluR5 has a significant positive impact in mice with ALS and support the idea that blocking Group I mGluRs may represent a potentially effective pharmacological approach to the disease.

Riluzole But Not Melatonin Ameliorates Acute Motor Neuron Degeneration and Moderately Inhibits SOD1-Mediated Excitotoxicity Induced Disrupted Mitochondrial Ca2+ Signaling in Amyotrophic Lateral Sclerosis

Selective motoneurons (MNs) degeneration in the brain stem, hypoglossal motoneurons (HMNs), and the spinal cord resulting in patients paralysis and eventual death are prominent features of amyotrophic lateral sclerosis (ALS). Previous studies have suggested that mitochondrial respiratory impairment, low Ca²⁺ buffering and homeostasis and excitotoxicity are the pathological phenotypes found in mice, and cell culture models of familial ALS (fALS) linked with Cu/Zn-superoxide dismutase 1 (SOD1) mutation. In our study, we aimed to understand the impact of riluzole and melatonin on excitotoxicity, neuronal protection and Ca²⁺ signaling in individual HMNs ex vivo in symptomatic adult ALS mouse brain stem slice preparations and in WT and SOD1-G93A transfected SH-SY5Y neuroblastoma cell line using fluorescence microscopy, calcium imaging with high speed charged coupled device camera, together with immunohistochemistry, cell survival assay and histology. In our experiments, riluzole but not melatonin ameliorates MNs degeneration and moderately inhibit excitotoxicity and cell death in SH-SY5Y^WT or SH-SY5Y^G93A cell lines induced by complex IV blocker sodium azide. In brain stem slice preparations, riluzole significantly inhibit HMNs cell death induced by inhibiting the mitochondrial electron transport chain by Na-azide. In the HMNs of brainstem slice prepared from adult (14–15 weeks) WT, and corresponding symptomatic SOD1^G93A mice, we measured the effect of riluzole and melatonin on [Ca²⁺]_i using fura-2 AM ratiometric calcium imaging in individual MNs. Riluzole caused a significant decrease in [Ca²⁺]_i transients and reversibly inhibited [Ca²⁺]_i transients in Fura-2 AM loaded HMNs exposed to Na-azide in adult symptomatic SOD1^G93A mice. On the contrary, melatonin failed to show similar effects in the HMNs of WT and SOD1^G93A mice. Intrinsic nicotinamide adenine dinucleotide (NADH) fluorescence, an indicator of mitochondrial metabolism and health in MNs, showed enhanced intrinsic NADH fluorescence in HMNs in presence of riluzole when respiratory chain activity was inhibited by Na-azide. Riluzole’s inhibition of excitability and Ca²⁺ signaling may be due to its multiple effects on cellular function of mitochondria. Therefore formulating a drug therapy to stabilize mitochondria-related signaling pathways using riluzole might be a valuable approach for cell death protection in ALS. Taken together, the pharmacological profiles of the riluzole and melatonin strengthen the case that riluzole indeed can be used as a therapeutic agent in ALS whereas claims of the efficacy of melatonin alone need further investigation as it fail to show significant neuroprotection efficacy.

MicroRNA-125b regulates microglia activation and motor neuron death in ALS

Understanding the means by which microglia self-regulate the neuroinflammatory response helps modulating their reaction during neurodegeneration. In amyotrophic lateral sclerosis (ALS), classical NF-κB pathway is related to persistent microglia activation and motor neuron injury; however, mechanisms of negative control of NF-κB activity remain unexplored. One of the major players in the termination of classical NF-κB pathway is the ubiquitin-editing enzyme A20, which has recognized anti-inflammatory functions. Lately, microRNAs are emerging as potent fine-tuners of neuroinflammation and reported to be regulated in ALS, for instance, by purinergic P2X7 receptor activation. In this work, we uncover an interplay between miR-125b and A20 protein in the modulation of classical NF-κB signaling in microglia. In particular, we establish the existence of a pathological circuit in which termination of A20 function by miR-125b strengthens and prolongs the noxious P2X7 receptor-dependent activation of NF-κB in microglia, with deleterious consequences on motor neurons. We prove that, by restoring A20 levels, miR-125b inhibition then sustains motor neuron survival. These results introduce miR-125b as a key mediator of microglia dynamics in ALS.

Mitochondrial dysfunction in amyotrophic lateral sclerosis - a valid pharmacological target?

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by the selective death of upper and lower motor neurons which ultimately leads to paralysis and ultimately death. Pathological changes in ALS are closely associated with pronounced and progressive changes in mitochondrial morphology, bioenergetics and calcium homeostasis. Converging evidence suggests that impaired mitochondrial function could be pivotal in the rapid neurodegeneration of this condition. In this review, we provide an update of recent advances in understanding mitochondrial biology in the pathogenesis of ALS and highlight the therapeutic value of pharmacologically targeting mitochondrial biology to slow disease progression.

Motor unit

Movement is accomplished by the controlled activation of motor unit populations. Our understanding of motor unit physiology has been derived from experimental work on the properties of single motor units and from computational studies that have integrated the experimental observations into the function of motor unit populations. The article provides brief descriptions of motor unit anatomy and muscle unit properties, with more substantial reviews of motoneuron properties, motor unit recruitment and rate modulation when humans perform voluntary contractions, and the function of an entire motor unit pool. The article emphasizes the advances in knowledge on the cellular and molecular mechanisms underlying the neuromodulation of motoneuron activity and attempts to explain the discharge characteristics of human motor units in terms of these principles. A major finding from this work has been the critical role of descending pathways from the brainstem in modulating the properties and activity of spinal motoneurons. Progress has been substantial, but significant gaps in knowledge remain.

The wobbler mouse, an ALS animal model

This review article is focused on the research progress made utilizing the wobbler mouse as animal model for human motor neuron diseases, especially the amyotrophic lateral sclerosis (ALS). The wobbler mouse develops progressive degeneration of upper and lower motor neurons and shows striking similarities to ALS. The cellular effects of the wobbler mutation, cellular transport defects, neurofilament aggregation, neuronal hyperexcitability and neuroinflammation closely resemble human ALS. Now, 57 years after the first report on the wobbler mouse we summarize the progress made in understanding the disease mechanism and testing various therapeutic approaches and discuss the relevance of these advances for human ALS. The identification of the causative mutation linking the wobbler mutation to a vesicle transport factor and the research focussed on the cellular basis and the therapeutic treatment of the wobbler motor neuron degeneration has shed new light on the molecular pathology of the disease and might contribute to the understanding the complexity of ALS.

Role of the N-methyl-d-aspartate receptors complex in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disease pathologically characterized by the massive loss of motor neurons in the spinal cord, brain stem and cerebral cortex. There is a consensus in the field that ALS is a multifactorial pathology and a number of possible mechanisms have been suggested. Among the proposed hypothesis, glutamate toxicity has been one of the most investigated. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor mediated cell death and impairment of the glutamate-transport system have been suggested to play a central role in the glutamate-mediated motor neuron degeneration. In this context, the role played by the N-methyl-d-aspartate (NMDA) receptor has received considerable less attention notwithstanding its high Ca(2+) permeability, expression in motor neurons and its importance in excitotoxicity. This review overviews the critical role of NMDA-mediated toxicity in ALS, with a particular emphasis on the endogenous modulators of the NMDAR.

Over-expression of N-type calcium channels in cortical neurons from a mouse model of Amyotrophic Lateral Sclerosis

Voltage-gated Ca(2+) channels (VGCCs) mediate calcium entry into neuronal cells in response to membrane depolarisation and play an essential role in a variety of physiological processes. In Amyotrophic Lateral Sclerosis (ALS), a fatal neurodegenerative disease caused by motor neuron degeneration in the brain and spinal cord, intracellular calcium dysregulation has been shown, while no studies have been carried out on VGCCs. Here we show that the subtype N-type Ca(2+) channels are over expressed in G93A cultured cortical neurons and in motor cortex of G93A mice compared to Controls. In fact, by western blotting, immunocytochemical and electrophysiological experiments, we observe higher membrane expression of N-type Ca(2+) channels in G93A neurons compared to Controls. G93A cortical neurons filled with calcium-sensitive dye Fura-2, show a net calcium entry during membrane depolarization that is significantly higher compared to Control. Analysis of neuronal vitality following the exposure of neurons to a high K(+) concentration (25 mM, 5h), shows a significant reduction of G93A cellular survival compared to Controls. N-type channels are involved in the G93A higher mortality because ω-conotoxin GVIA (1 μM), which selectively blocks these channels, is able to abolish the higher G93A mortality when added to the external medium. These data provide robust evidence for an excess of N-type Ca(2+) expression in G93A cortical neurons which induces a higher mortality following membrane depolarization. These results may be central to the understanding of pathogenic pathways in ALS and provide novel molecular targets for the design of rational therapies for the ALS disorder.

Mitochondrial Ca(2+) and neurodegeneration

Mitochondria are essential for ensuring numerous fundamental physiological processes such as cellular energy, redox balance, modulation of Ca²⁺ signaling and important biosynthetic pathways. They also govern the cell fate by participating in the apoptosis pathway.

The mitochondrial shape, volume, number and distribution within the cells are strictly controlled. The regulation of these parameters has an impact on mitochondrial function, especially in the central nervous system, where trafficking of mitochondria is critical to their strategic intracellular distribution, presumably according to local energy demands. Thus, the maintenance of a healthy mitochondrial population is essential to avoid the impairment of the processes they regulate: for this purpose, cells have developed mechanisms involving a complex system of quality control to remove damaged mitochondria, or to renew them. Defects of these processes impair mitochondrial function and lead to disordered cell function, i.e., to a disease condition. Given the standard role of mitochondria in all cells, it might be expected that their dysfunction would give rise to similar defects in all tissues. However, damaged mitochondrial function has pleiotropic effects in multicellular organisms, resulting in diverse pathological conditions, ranging from cardiac and brain ischemia, to skeletal muscle myopathies to neurodegenerative diseases. In this review, we will focus on the relationship between mitochondrial (and cellular) derangements and Ca²⁺ dysregulation in neurodegenerative diseases, emphasizing the evidence obtained in genetic models. Common patterns, that recognize the derangement of Ca²⁺ and energy control as a causative factor, have been identified: advances in the understanding of the molecular regulation of Ca²⁺ homeostasis, and on the ways in which it could become perturbed in neurological disorders, may lead to the development of therapeutic strategies that modulate neuronal Ca²⁺ signaling.

Protein repertoire impact of Ubiquitin-Proteasome System impairment: insight into the protective role of beta-estradiol

The Ubiquitin-Proteasome System (UPS) and the Autophagy-Lysosome Pathways (ALP) are key mechanisms for cellular homeostasis sustenance and protein clearance. A wide number of Neurodegenerative Diseases (NDs) are tied with UPS impairment and have been also described as proteinopathies caused by aggregate-prone proteins, not efficiently removed by proteasome. Despite the large knowledge on proteasome biological role, molecular mechanisms associated with its impairment are still blur. We have pursued a comprehensive proteomic investigation to evaluate the phenotypic rearrangements in protein repertoires associated with a UPS blockage. Different functional proteomic approaches have been employed to tackle UPS impairment impact on human NeuroBlastoma (NB) cell lines responsive to proteasome inhibition by Epoxomicin. 2-Dimensional Electrophoresis (2-DE) separation combined with Mass Spectrometry and Shotgun Proteomics experiments have been employed to design a thorough picture of protein profile. Unsupervised meta-analysis of the collected proteomic data revealed that all the identified proteins relate each other in a functional network centered on beta-estradiol. Moreover we showed that treatment of cells with beta-estradiol resulted in aggregate removal and increased cell survival due to activation of the autophagic pathway. Our data may provide the molecular basis for the use of beta-estradiol in neurodegenerative disorders by induction of protein aggregate removal.

Increased expression of the beta3 subunit of voltage-gated Na+ channels in the spinal cord of the SOD1G93A mouse

Amyotrophic lateral sclerosis (ALS) is an adult-onset disease characterized by the progressive degeneration of motoneurons (MNs). Altered electrical properties have been described in familial and sporadic ALS patients. Cortical and spinal neurons cultured from the mutant Cu,Zn superoxide dismutase 1 (SOD1G93A) mouse, a murine model of ALS, exhibit a marked increase in the persistent Na+ currents. Here, we investigated the effects of the SOD1G93A mutation on the expression of the voltage-gated Na+ channel alpha subunit SCN8A (Nav1.6) and the beta subunits SCN1B (beta1), SCN2B (beta2), and SCN3B (beta3) in MNs of the spinal cord in presymptomatic (P75) and symptomatic (P120) mice. We observed a significant increase, within lamina IX, of the beta3 transcript and protein expression. On the other hand, the beta1 transcript was significantly decreased, in the same area, at the symptomatic stage, while the beta2 transcript levels were unaltered. The SCN8A transcript was significantly decreased at P120 in the whole spinal cord. These data suggest that the SOD1G93A mutation alters voltage-gated Na+ channel subunit expression. Moreover, the increased expression of the beta3 subunit support the hypothesis that altered persistent Na+ currents contribute to the hyperexcitability observed in the ALS-affected MNs.

New therapeutic targets for amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is one of the most devastating neurological disorders, affecting approximately half a million people worldwide. Currently there is no cure or prevention for ALS. Although ALS is a rare condition, it places a tremendous socioeconomic burden on patients, family members, caregivers and health systems.

AREAS COVERED

The review examines the mechanisms that may contribute to motor neuron degeneration in ALS, among which oxidative damage, glutatamate excitoxicity, mitochondrial dysfunction, impaired axonal transport, apoptotic cell death, growth factor deficiency, glial cell pathology and abnormal RNA metabolism are potential targets for ALS treatment. The article provides an overview of clinical trials performed to date in attempts to treat ALS with regard to molecular mechanisms and pathways they act on. It also discusses new trials based on recently developed molecular biology techniques.

EXPERT OPINION

Despite significant effectiveness of several potential therapeutics observed in preclinical trials, the results were not translatable to patients with ALS. The development of effective treatments of ALS strictly depends on understanding the primary cause of the disease. This goal will only be achieved when we identify the trigger point for motor neuron death in ALS.

Zinc pre-treatment enhances NMDAR-mediated excitotoxicity in cultured cortical neurons from SOD1(G93A) mouse, a model of amyotrophic lateral sclerosis

Zn²+ is co-released at glutamatergic synapses throughout the central nervous system and acts as a neuromodulator for glutamatergic neurotransmission, as a key modulator of NMDA receptor functioning. Zn²+ is also implicated in the neurotoxicity associated with several models of acute brain injury and neurodegeneration. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting motor neurons in the spinal cord and cortex. In this study, we have investigated the modulatory role exerted by Zn²+ in NMDA-mediated neurotoxicity in either near-pure or mixed cortical cultured neurons obtained from either mice over-expressing the G93A mutant form of Cu/Zn superoxide dismutase (SOD1) human gene, a gene linked to familial ALS, or wild type (WT) mice. To that aim, SOD1(G93A) or WT cultures were exposed to either NMDA by itself or to Zn²+ prior to a toxic challenge with NMDA, and neuronal loss evaluated 24 h later. While we failed to observe any significant difference between NMDA and Zn²+/NMDA-mediated toxicity in mixed SOD1(G93A) or WT cortical cultures, different vulnerability to these toxic paradigms was found in near-pure neuronal cultures. In the WT near-pure neuronal cultures, a brief exposure to sublethal concentrations of Zn²+-enhanced NMDA receptor-mediated cell death, an effect that was far more pronounced in the SOD1(G93A) cultures. This increased excitotoxicity in SOD1(G93A) near-pure neuronal cultures appears to be mediated by a significant increase in NMDA-dependent rises of intraneuronal Ca²+ levels as well as enhanced production of cytosolic reactive oxygen species, while the injurious process seems to be unrelated to activation of nNOS or ERK1/2 pathways. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Postsynaptic alteration of NR2A subunit and defective autophosphorylation of alphaCaMKII at threonine-286 contribute to abnormal plasticity and morphology of upper motor neurons in presymptomatic SOD1G93A mice, a murine model for amyotrophic lateral sclerosis

Although amyotrophic lateral sclerosis (ALS) has long been considered as a lower motor neuron (MN) disease, degeneration of upper MNs arising from a combination of mechanisms including insufficient growth factor signaling and enhanced extracellular glutamate levels is now well documented. The observation that these mechanisms are altered in presymptomatic superoxide dismutase (SOD1) mice, an ALS mouse model, suggests that defective primary motor cortex (M1) synaptic activity might precede the onset of motor disturbances. To examine this point, we assessed the composition of AMPAR and NMDAR subunits and of the alphaCa²(+)/calmodulin-dependent kinase autophosphorylation at threonine-286 in the triton insoluble fraction from the M1 in postnatal P80-P85 SOD1(G93A) and wild-type mice. We show that presymptomatic SOD1(G93A) exhibit a selective decrease of NR2A subunit expression and of the alphaCa²(+)/calmodulin-dependent kinase autophosphorylation at threonine-286 in the triton insoluble fraction of upper MNs synapses. These molecular alterations are associated with synaptic plasticity defects, and a reduction in upper MN dendritic outgrowth revealing that abnormal neuronal connectivity in the M1 region precedes the onset of motor symptoms. We suggest that the progressive disruption of M1 corticocortical connections resulting from the SOD1(G93A) mutation might extend to adjacent regions and promote development of cognitive/dementia alterations frequently associated with ALS.

Vascular endothelial growth factor prevents G93A-SOD1-induced motor neuron degeneration

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder characterized by selective loss of motor neurons (MNs). Twenty percent of familial ALS cases are associated with mutations in Cu(2+)/Zn(2+) superoxide dismutase (SOD1). To specifically understand the cellular mechanisms underlying mutant SOD1 toxicity, we have established an in vitro model of ALS using rat primary MN cultures transfected with an adenoviral vector encoding a mutant SOD1, G93A-SOD1. Transfected cells undergo axonal degeneration and alterations in biochemical responses characteristic of cell death such as activation of caspase-3. Vascular endothelial growth factor (VEGF) is an angiogenic and neuroprotective growth factor that can increase axonal outgrowth, block neuronal apoptosis, and promote neurogenesis. Decreased VEGF gene expression in mice results in a phenotype similar to that seen in patients with ALS, thus linking loss of VEGF to the pathogenesis of MN degeneration. Decreased neurotrophic signals prior to and during disease progression may increase MN susceptibility to mutant SOD1-induced toxicity. In this study, we demonstrate a decrease in VEGF and VEGFR2 levels in the spinal cord of G93A-SOD1 ALS mice. Furthermore, in isolated MN cultures, VEGF alleviates the effects of G93A-SOD1 toxicity and neuroprotection involves phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling. Overall, these studies validate the usefulness of VEGF as a potential therapeutic factor for the treatment of ALS and give valuable insight into the responsible signaling pathways and mechanisms involved.

GAB(A) receptors present higher affinity and modified subunit composition in spinal motor neurons from a genetic model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a neurodegenerative disease characterized by the selective degeneration of motor neurons in the spinal cord, brainstem and cerebral cortex. In this study we have analysed the electrophysiological properties of GABA(A) receptors and GABA(A) alpha1 and alpha2 subunits expression in spinal motor neurons in culture obtained from a genetic model of ALS (G93A) and compared with transgenic wild type SOD1 (SOD1) and their corresponding non transgenic litter mates (Control). Although excitotoxic motor neuron death has been extensively studied in relation to Ca(2+)-dependent processes, strong evidence indicates that excitotoxic cell death is also remarkably dependent on Cl(-) ions and on GABA(A) receptor activation. In this study we have analysed the electrophysiological properties of GABA(A) receptors and the expression of GABA(A)alpha(1) and alpha(2) subunits in cultured motor neurons obtained from a genetic model of amyotrophic lateral sclerosis (G93A) and compared them with transgenic wild-type Cu,Zn superoxide dismutase and their corresponding non-transgenic littermates (Control). In all tested motor neurons, the application of gamma-aminobutyric acid (GABA) (0.5-100 mum) evoked an inward current that was reversibly blocked by bicuculline (100 mum), thus indicating that it was mediated by the activation of GABA(A) receptors. Our results indicate that the current density at high GABA concentrations is similar in control, Cu,Zn superoxide dismutase and G93A motor neurons. However, the dose-response curve significantly shifted toward lower concentration values in G93A motor neurons and the extent of desensitization also increased in these neurons. Finally, multiplex single-cell real-time polymerase chain reaction and immunofluorescence revealed that the amount of GABA(A)alpha(1) subunit was significantly increased in G93A motor neurons, whereas the levels of alpha(2) subunit were unchanged. These data show that the functionality and expression of GABA(A) receptors are altered in G93A motor neurons inducing a higher Cl(-) influx into the cell with a possible consequent neuronal excitotoxicity acceleration.

A beta-lactam antibiotic dampens excitotoxic inflammatory CNS damage in a mouse model of multiple sclerosis

In multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE), impairment of glial “Excitatory Amino Acid Transporters” (EAATs) together with an excess glutamate-release by invading immune cells causes excitotoxic damage of the central nervous system (CNS). In order to identify pathways to dampen excitotoxic inflammatory CNS damage, we assessed the effects of a β-lactam antibiotic, ceftriaxone, reported to enhance expression of glial EAAT2, in “Myelin Oligodendrocyte Glycoprotein” (MOG)-induced EAE. Ceftriaxone profoundly ameliorated the clinical course of murine MOG-induced EAE both under preventive and therapeutic regimens. However, ceftriaxone had impact neither on EAAT2 protein expression levels in several brain areas, nor on the radioactive glutamate uptake capacity in a mixed primary glial cell-culture and the glutamate-induced uptake currents in a mammalian cell line mediated by EAAT2. Moreover, the clinical effect of ceftriaxone was preserved in the presence of the EAAT2-specific transport inhibitor, dihydrokainate, while dihydrokainate alone caused an aggravated EAE course. This demonstrates the need for sufficient glial glutamate uptake upon an excitotoxic autoimmune inflammatory challenge of the CNS and a molecular target of ceftriaxone other than the glutamate transporter. Ceftriaxone treatment indirectly hampered T cell proliferation and proinflammatory INFγ and IL17 secretion through modulation of myelin-antigen presentation by antigen-presenting cells (APCs) e.g. dendritic cells (DCs) and reduced T cell migration into the CNS in vivo. Taken together, we demonstrate, that a β-lactam antibiotic attenuates disease course and severity in a model of autoimmune CNS inflammation. The mechanisms are reduction of T cell activation by modulation of cellular antigen-presentation and impairment of antigen-specific T cell migration into the CNS rather than or modulation of central glutamate homeostasis.

Lithium delays progression of amyotrophic lateral sclerosis

ALS is a devastating neurodegenerative disorder with no effective treatment. In the present study, we found that daily doses of lithium, leading to plasma levels ranging from 0.4 to 0.8 mEq/liter, delay disease progression in human patients affected by ALS. None of the patients treated with lithium died during the 15 months of the follow-up, and disease progression was markedly attenuated when compared with age-, disease duration-, and sex-matched control patients treated with riluzole for the same amount of time. In a parallel study on a genetic ALS animal model, the G93A mouse, we found a marked neuroprotection by lithium, which delayed disease onset and duration and augmented the life span. These effects were concomitant with activation of autophagy and an increase in the number of the mitochondria in motor neurons and suppressed reactive astrogliosis. Again, lithium reduced the slow necrosis characterized by mitochondrial vacuolization and increased the number of neurons counted in lamina VII that were severely affected in saline-treated G93A mice. After lithium administration in G93A mice, the number of these neurons was higher even when compared with saline-treated WT. All these mechanisms may contribute to the effects of lithium, and these results offer a promising perspective for the treatment of human patients affected by ALS.

Altered calcium homeostasis in motor neurons following AMPA receptor but not voltage-dependent calcium channels' activation in a genetic model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive neurodegenerative disease characterized by a substantial loss of motor neurons in the spinal cord, brain stem and motor cortex. By combining electrophysiological recordings with imaging techniques, clearance/buffering capacity of cultured spinal cord motor neurons after a calcium accumulation has been analyzed in response to AMPA receptors' (AMPARs') activation and to depolarizing stimuli in a genetic mouse model of ALS (G93A). Our studies demonstrate that the amplitude of the calcium signal in response to AMPARs' or voltage-dependent calcium channels' activation is not significantly different in controls and G93A motor neurons. On the contrary, in G93A motor neurons, the [Ca(2+)](i) recovery to basal level is significantly slower compared to control neurons following AMPARs but not voltage-dependent calcium channels' activation. This difference was not observed in G93A cultured cortical neurons. This observation is the first to indicate a specific alteration of the calcium clearance linked to AMPA receptors' activation in G93A motor neurons and the involvement of AMPA receptor regulatory proteins controlling both AMPA receptor functionality and the sequence of events connected to them.

Toxicity from different SOD1 mutants dysregulates the complement system and the neuronal regenerative response in ALS motor neurons

Global, age-dependent changes in gene expression from rodent models of inherited ALS caused by dominant mutations in superoxide-dismutase 1 (SOD1) were identified by using gene arrays and RNAs isolated from purified embryonic and adult motor neurons. Comparison of embryonic motor neurons expressing a dismutase active ALS-linked mutant SOD1 with those expressing comparable levels of wild-type SOD1 revealed the absence of mutant-induced mRNA changes. An age-dependent mRNA change that developed presymptomatically in adult motor neurons collected by laser microdissection from mice expressing dismutase active ALS-linked mutants was dysregulation of the d/l-serine biosynthetic pathway, previously linked to both excitotoxic and neurotrophic effects. An unexpected dysregulation common to motor neurons expressing either dismutase active or inactive mutants was induction of neuronally derived components of the classic complement system and the regenerative/injury response. Alteration of these mutant SOD1-induced pathways identified a set of targets for therapies for inherited ALS.

Voltage-Dependent Sodium Channels in Spinal Cord Motor Neurons Display Rapid Recovery From Fast Inactivation in a Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by a substantial loss of motor neurons in the spinal cord, brain stem, and motor cortex. Previous evidence showed that in a mouse model of a familial form of ALS expressing high levels of the human mutated protein Cu,Zn superoxide dismutase (Gly93→Ala, G93A), the firing properties of single motor neurons are altered to induce neuronal hyperexcitability. To determine whether the functionality of the macroscopic voltage-dependent Na+ currents is modified in G93A motor neurons, in the present work their physiological properties were examined. The voltage-dependent sodium channels were studied in dissociated motor neurons in culture from nontransgenic mice (Control), from transgenic mice expressing high levels of the human wild-type protein [superoxide dismutase 1 (SOD1)], and from G93A mice, using the whole cell configuration of the patch-clamp recording technique. The voltage dependency of activation and of steady-state inactivation, the kinetics of fast inactivation and slow inactivation of the voltage-dependent Na+ channels were not modified in the mutated mice. Conversely, the recovery from fast inactivation was significantly faster in G93A motor neurons than that in Control and SOD1. The recovery from fast inactivation was still significantly faster in G93A motor neurons exposed for different times (3–48 h) and concentrations (5–500 μM) to edaravone, a free-radical scavenger. Clarification of the importance of these changes in membrane ion channel functionality may have diagnostic and therapeutic implications in the pathogenesis of ALS.

ALS: a disease of motor neurons and their nonneuronal neighbors

Amyotrophic lateral sclerosis is a late-onset progressive neurodegenerative disease affecting motor neurons. The etiology of most ALS cases remains unknown, but 2% of instances are due to mutations in Cu/Zn superoxide dismutase (SOD1). Since sporadic and familial ALS affects the same neurons with similar pathology, it is hoped that therapies effective in mutant SOD1 models will translate to sporadic ALS. Mutant SOD1 induces non-cell-autonomous motor neuron killing by an unknown gain of toxicity. Selective vulnerability of motor neurons likely arises from a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, defective axonal transport, excitotoxicity, insufficient growth factor signaling, and inflammation. Damage within motor neurons is enhanced by damage incurred by nonneuronal neighboring cells, via an inflammatory response that accelerates disease progression. These findings validate therapeutic approaches aimed at nonneuronal cells.

Slow and selective death of spinal motor neurons in vivo by intrathecal infusion of kainic acid: implications for AMPA receptor-mediated excitotoxicity in ALS

Excitotoxicity mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors has been proposed to play a major role in the selective death of motor neurons in sporadic amyotrophic lateral sclerosis (ALS), and motor neurons are more vulnerable to AMPA receptor-mediated excitotoxicity than are other neuronal subclasses. On the basis of the above evidence, we aimed to develop a rat model of ALS by the long-term activation of AMPA receptors through continuous infusion of kainic acid (KA), an AMPA receptor agonist, into the spinal subarachnoid space. These rats displayed a progressive motor-selective behavioral deficit with delayed loss of spinal motor neurons, mimicking the clinicopathological characteristics of ALS. These changes were significantly ameliorated by co-infusion with 6-nitro-7-sulfamobenso(f)quinoxaline-2,3-dione (NBQX), but not with d(-)-2-amino-5-phosphonovaleric acid (APV), and were exacerbated by co-infusion with cyclothiazide, indicative of an AMPA receptor-mediated mechanism. Among the four AMPA receptor subunits, expression of GluR3 mRNA was selectively up-regulated in motor neurons but not in dorsal horn neurons of the KA-infused rats. The up-regulation of GluR3 mRNA in this model may cause a molecular change that induces the selective vulnerability of motor neurons to KA by increasing the proportion of GluR2-lacking (i.e. calcium-permeable) AMPA receptors. This rat model may be useful in investigating ALS etiology.

Targets in ALS: designing multidrug therapies

Amyotrophic lateral sclerosis (ALS) is an incurable disease that arises from the progressive loss of motoneurons. Even when caused by a single gene defect, as in the case of mutations in the enzyme Cu-Zn superoxide dismutase (SOD1), ALS is the result of a complex cascade that involves crosstalk among motoneurons, glia and muscles, and evolves through the action of converging toxic mechanisms. Transgenic rodents that express human mutant SOD1 and develop a progressive paralytic disease are widely used to screen potential therapeutics. Treatments that interfere with a specific event in the neurotoxic cascade have been reported to produce a modest increase in rodent lifespan. Multi-intervention approaches, including novel methods to intercept the damage and to deliver molecules to vulnerable cells, have recently been shown to be more effective. Thus, new avenues for promising therapeutic approaches can be derived from multidrug treatments and/or the delivery of growth factors by viral vectors, in combination with exercise and/or diet regimens.

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.

Early abnormalities in transgenic mouse models of amyotrophic lateral sclerosis

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

Excitotoxicity and ALS: what is unique about the AMPA receptors expressed on spinal motor neurons?

It has been repeatedly reported that spinal motor neurons are selectively vulnerable to AMPA receptor-mediated excitotoxicity. Therefore, identifying the uniqueness of AMPA receptors that are expressed on motor neurons, especially in individuals affected with sporadic amyotrophic lateral sclerosis (ALS) is essential for elucidating the etiology of this disorder. The mechanism that initiates motor neuronal death appears to be an exaggerated influx of Ca(2+) through AMPA receptors. The determinants that affect this Ca(2+) influx are Ca(2+) permeability, which is regulated by the presence of the GluR2 subunit and by RNA editing at the Q/R site of GluR2; channel desensitization, which is regulated by alternative splicing at the flip/flop site and by RNA editing at the R/G site of GluR subunits; and receptor density on the cell surface, which is controlled by many factors including regulatory proteins, direct phosphorylation and RNA editing at the Q/R site. This review focuses on recent progress on the molecular dynamics of AMPA receptors and discusses the pathophysiology of selective motor neuron death mediated by AMPA receptors in individuals affected with sporadic ALS.