Abnormal excitatory amino acid metabolism in amyotrophic lateral sclerosis

Regulation of nuclear TDP-43 by NR2A-containing NMDA receptors and PTEN

The dysfunction of TAR DNA-binding protein-43 (TDP-43) is implicated in neurodegenerative diseases. However, the function of TDP-43 is not fully elucidated. Here we show that the protein level of endogenous TDP-43 in the nucleus is increased in mouse cortical neurons in the early stages, but return to basal level in the later stages after glutamate accumulation-induced injury. The elevation of TDP-43 results from a downregulation of phosphatase and tensin homolog (PTEN). We further demonstrate that activation of NR2A-containing NMDA receptors (NR2ARs) leads to PTEN downregulation and subsequent reduction of PTEN import from the cytoplasm to the nucleus after glutamate accumulation. The decrease of PTEN in the nucleus contributes to its reduced association with TDP-43, and thereby mediates the elevation of nuclear TDP-43. We provide evidence that the elevation of nuclear TDP-43, mediated by NR2AR activation and PTEN downregulation, confers protection against cortical neuronal death in the late stages after glutamate accumulation. Thus, this study reveals a NR2AR-PTEN-TDP-43 signaling pathway by which nuclear TDP-43 promotes neuronal survival. These results suggest that upregulation of nuclear TDP-43 represents a self-protection mechanism to delay neurodegeneration in the early stages after glutamate accumulation and that prolonging the upregulation process of nuclear TDP-43 might have therapeutic significance.

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.

Changes in the astrocytic aquaporin-4 and inwardly rectifying potassium channel expression in the brain of the amyotrophic lateral sclerosis SOD1(G93A) rat model

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting upper and lower motor neurons. Dysfunction and death of motor neurons are closely related to the modified astrocytic environment. Astrocytic endfeet, lining the blood-brain barrier (BBB), are enriched in two proteins, aquaporin-4 (AQP4) and inwardly rectifying potassium channel (Kir) 4.1. Both channels are important for the maintainance of a functional BBB astrocytic lining. In this study, expression levels of AQP4 and Kir4.1 were for the first time examined in the brainstem and cortex, along with the functional properties of Kir channels in cultured cortical astrocytes of the SOD1(G93A) rat model of ALS. Western blot analysis showed increased expression of AQP4 and decreased expression of Kir4.1 in the brainstem and cortex of the ALS rat. In addition, higher immunoreactivity of AQP4 and reduced immunolabeling of Kir4.1 in facial and trigeminal nuclei as well as in the motor cortex were also observed. Particularly, the observed changes in the expression of both channels were retained in cultured astrocytes. Furthermore, whole-cell patch-clamp recordings from cultured ALS cortical astrocytes showed a significantly lower Kir current density. Importantly, the potassium uptake current in ALS astrocytes was significantly reduced at all extracellular potassium concentrations. Consequently, the Kir-specific Cs(+)- and Ba(2+)-sensitive currents were also decreased. The changes in the studied channels, notably at the upper CNS level, could underline the hampered ability of astrocytes to maintain water and potassium homeostasis, thus affecting the BBB, disturbing the neuronal microenvironment, and causing motoneuronal dysfunction and death.

UNC13A influences survival in Italian amyotrophic lateral sclerosis patients: a population-based study

The common variant rs12608932, located within an intron of UNC13A gene on chromosome 19p13.3, has been suggested to influence susceptibility to amyotrophic lateral sclerosis (ALS), as well as survival, in patients of north European descent. To examine this possibility further, we evaluated the association of rs12608932 with susceptibility and survival in a population-based cohort of 500 Italian ALS patients and 1457 Italian control samples. Although rs12608932 was not associated with ALS susceptibility in our series (p = 0.124), it was significantly associated with survival under the recessive model (median survival for AA/AC genotypes = 3.5 years [interquartile range, 2.2-6.4]; CC = 2.5 years [interquartile range, 1.6-4.2]; p = 0.017). Furthermore, rs12608932 genotype remained an independent prognostic factor in Cox multivariable analysis adjusting for other factors known to influence survival (p = 0.023). Overall, minor allele carrier status of rs12608932 was strongly associated with an approximate 1-year reduction of survival in ALS patients, making it a significant determinant of phenotype variation. The identification of UNC13A as a modifier of prognosis among sporadic ALS patients potentially provides a new therapeutic target aimed at slowing disease progression.

Impairments to the GH-IGF-I axis in hSOD1G93A mice give insight into possible mechanisms of GH dysregulation in patients with amyotrophic lateral sclerosis

GH deficiency has been found in subjects with amyotrophic lateral sclerosis (ALS). Disrupted endocrine function could contribute to the progressive muscle loss and hypermetabolism seen in ALS. It is not possible to study all the elements of the GH-IGF-I axis in ALS patients. Consequently, it remains unclear whether dysfunctional GH secretion contributes to disease pathogenesis and why GH and IGF-I directed treatment strategies are ineffective in human ALS. The hSOD1(G93A) transgenic mouse model is useful for the detailed investigation of the pathogenesis of ALS. We report that symptomatic male hSOD1(G93A) transgenic mice exhibit a deficiency in GH secretion similar to that seen in human ALS. Further characterization of the GH-IGF-I axis in hSOD1(G93A) mice reveals central and peripheral abnormalities that are not found in wild-type age-matched controls. Specifically, we observe aberrant endogenous pulsatile GH secretion, reduced pituitary GH content, and decreased circulating levels of IGF-I, indicating global GH deficiency in hSOD1(G93A) mice. Furthermore, a reduction in the expression of the IGF-I receptor α-subunit in skeletal muscle and lumbar spinal cords of hSOD1(G93A) mice suggests impaired IGF-I signaling within these tissues. This is the first account of disrupted GH secretion in a transgenic mouse model of ALS. These observations are essential for the development of effective GH and IGF-I targeted therapies in ALS.

Calpains are downstream effectors of bax-dependent excitotoxic apoptosis

Excitotoxicity resulting from excessive Ca(2+) influx through glutamate receptors contributes to neuronal injury after stroke, trauma, and seizures. Increased cytosolic Ca(2+) levels activate a family of calcium-dependent proteases with papain-like activity, the calpains. Here we investigated the role of calpain activation during NMDA-induced excitotoxic injury in embryonic (E16-E18) murine cortical neurons that (1) underwent excitotoxic necrosis, characterized by immediate deregulation of Ca(2+) homeostasis, a persistent depolarization of mitochondrial membrane potential (Δψ(m)), and insensitivity to bax-gene deletion, (2) underwent excitotoxic apoptosis, characterized by recovery of NMDA-induced cytosolic Ca(2+) increases, sensitivity to bax gene deletion, and delayed Δψ(m) depolarization and Ca(2+) deregulation, or (3) that were tolerant to excitotoxic injury. Interestingly, treatment with the calpain inhibitor calpeptin, overexpression of the endogenous calpain inhibitor calpastatin, or gene silencing of calpain protected neurons against excitotoxic apoptosis but did not influence excitotoxic necrosis. Calpeptin failed to exert a protective effect in bax-deficient neurons but protected bid-deficient neurons similarly to wild-type cells. To identify when calpains became activated during excitotoxic apoptosis, we monitored calpain activation dynamics by time-lapse fluorescence microscopy using a calpain-sensitive Förster resonance energy transfer probe. We observed a delayed calpain activation that occurred downstream of mitochondrial engagement and directly preceded neuronal death. In contrast, we could not detect significant calpain activity during excitotoxic necrosis or in neurons that were tolerant to excitotoxic injury. Oxygen/glucose deprivation-induced injury in organotypic hippocampal slice cultures confirmed that calpains were specifically activated during bax-dependent apoptosis and in this setting function as downstream cell-death executioners.

Coadministration of bicuculline and NMDA induces paraplegia in the rat

Motor neurons (MNs) of an adult rat are normally insensitive to the neurotoxic action of NMDA. Meanwhile, the experiments in non-motor neurons showed that sensitivity to NMDA can be increased by bicuculline, an antagonist at GABA(A) receptors. The aim of the present work was to examine whether bicuculline would produce such an effect in the adult MNs. In adult Wistar rats, intrathecal injection of bicuculline and NMDA individually failed to affect motor activity of the extremities. In contrast, bicuculline-NMDA combination dose-dependently impaired hindlimb functions. At the 9th day after injections of the combination, a paraplegia with persistent bilateral spastic extension developed in all animals. Light microscopic assessment showed that the development of the motor deficit is associated with pathological changes in spinal motor neurons (swelling, accumulation of the Nissl substance near nucleus, hyperchromatosis, shrinkage, and chromatolysis), mainly in the lumbar ventral horns. Additionally, distinct abnormalities were observed in the white matter of the lumbar cords. The bicuculline-NMDA combination induced a loss of spinal cord MNs while sparing the dorsal horn neurons. The effects of the combination were reversed by muscimol, a GABA(A) agonist. Thus, an inhibition of GABA(A)ergic processes can induce NMDA sensitivity in adult MNs. The present data may provide new insights into the mechanism of motor disorders in amyotrophic lateral sclerosis and other states wherein the combination of glutamatergic overstimulation and GABA(A)ergic understimulation takes place.

Paradoxical roles of serine racemase and D-serine in the G93A mSOD1 mouse model of amyotrophic lateral sclerosis

D-serine is an endogenous neurotransmitter that binds to the NMDA receptor, thereby increasing the affinity for glutamate, and the potential for excitotoxicity. The primary source of D-serine in vivo is enzymatic racemization by serine racemase (SR). Regulation of D-serine in vivo is poorly understood, but is thought to involve a combination of controlled production, synaptic reuptake by transporters, and intracellular degradation by D-amino acid oxidase (DAO). However, SR itself possesses a well-characterized eliminase activity, which effectively degrades D-serine as well. D-serine is increased two-fold in spinal cords of G93A Cu,Zn-superoxide dismutase (SOD1) mice--the standard model of amyotrophic lateral sclerosis (ALS). ALS mice with SR disruption show earlier symptom onset, but survive longer (progression phase is slowed), in an SR-dependent manner. Paradoxically, administration of D-serine to ALS mice dramatically lowers cord levels of D-serine, leading to changes in the onset and survival very similar to SR deletion. D-serine treatment also increases cord levels of the alanine-serine-cysteine transporter 1 (Asc-1). Although the mechanism by which SOD1 mutations increases D-serine is not known, these results strongly suggest that SR and D-serine are fundamentally involved in both the pre-symptomatic and progression phases of disease, and offer a direct link between mutant SOD1 and a glial-derived toxic mediator.

Proton MR spectroscopy-detectable major neurotransmitters of the brain: biology and possible clinical applications

Neurotransmitters are chemical substances that, by definition, allow communication between neurons and permit most neuronal-glial interactions in the CNS. Approximately 80% of all neurons use glutamate, and almost all interneurons use GABA. A third neurotransmitter, NAAG, modulates glutamatergic neurotransmission. Concentration changes in these molecules due to defective synthetic machinery, receptor expression, or errors in their degradation and metabolism are accepted causes of several neurologic disorders. Knowledge of changes in neurotransmitter concentrations in the brain can add useful information in making a diagnosis, helping to pick the right drug of treatment, and monitoring patient response to drugs in a more objective manner. Recent advances in (1)H-MR spectroscopy hold promise in providing a more reliable in vivo detection of these neurotransmitters. In this article, we summarize the essential biology of 3 major neurotransmitters: glutamate, GABA, and NAAG. Finally we illustrate possible applications of (1)H-MR spectroscopy in neuroscience research.

Molecular motor proteins and amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting motor neurons in the brain, brainstem and spinal cord, which is characterized by motor dysfunction, muscle dystrophy and progressive paralysis. Both inherited and sporadic forms of ALS share common pathological features, however, the initial trigger of neurodegeneration remains unknown. Motor neurons are uniquely targeted by ubiquitously expressed proteins in ALS but the reason for this selectively vulnerability is unclear. However motor neurons have unique characteristics such as very long axons, large cell bodies and high energetic metabolism, therefore placing high demands on cellular transport processes. Defects in cellular trafficking are now widely reported in ALS, including dysfunction to the molecular motors dynein and kinesin. Abnormalities to dynein in particular are linked to ALS, and defects in dynein-mediated axonal transport processes have been reported as one of the earliest pathologies in transgenic SOD1 mice. Furthermore, dynein is very highly expressed in neurons and neurons are particularly sensitive to dynein dysfunction. Hence, unravelling cellular transport processes mediated by molecular motor proteins may help shed light on motor neuron loss in ALS.

The preclinical discovery of amyotrophic lateral sclerosis drugs

INTRODUCTION

Amyotrophic lateral sclerosis (ALS), also referred to as Lou Gehrig's disease, is characterized by the progressive loss of cells in the brain and spinal cord that leads to debilitation and death in 3 - 5 years. Only one therapeutic drug, riluzole, has been approved for ALS and this drug improves survival by 2 - 3 months. The need for new therapeutics that can postpone or slow the progression of the motor deficits and prolong survival is still a strong unmet medical need.

AREAS COVERED

Although there are a number of drugs currently in clinical trials for ALS, this review provides an overview of the most promising biological targets and preclinical strategies that are currently being developed and deployed. The list of targets for ALS was compiled from a variety of websites including individual companies that have ALS programs and include those from the author's experience.

EXPERT OPINION

Progress is being made in the identification of possible new therapeutics for ALS with recent efforts in understanding the genetic causes of the disease, susceptibility factors and the development of additional preclinical animal models. However, many challenges remain in the identification of new ALS therapeutics including: the use of relevant biomarkers, the need for an earlier diagnosis of the disease and additional animal models. Multiple strategies need to be tested in the clinic in order to determine what will be effective in patients.

Cell stress induces TDP-43 pathological changes associated with ERK1/2 dysfunction: implications in ALS

TDP-43 has been implicated in the pathogenesis of amyotrophic lateral sclerosis and other neurodegenerative diseases. Here we demonstrate, using neuronal and spinal cord organotypic culture models, that chronic excitotoxicity, oxidative stress, proteasome dysfunction and endoplasmic reticulum stress mechanistically induce mislocalization, phosphorylation and aggregation of TDP-43. This is compatible with a lack of function of this protein in the nucleus, specially in motor neurons. The relationship between cell stress and pathological changes of TDP-43 also includes a dysfunction in the survival pathway mediated by mitogen-activated protein kinase/extracellular signal-regulated kinases (ERK1/2). Thus, under stress conditions, neurons and other spinal cord cells showed cytosolic aggregates containing ERK1/2. Moreover, aggregates of abnormal phosphorylated ERK1/2 were also found in the spinal cord in amyotrophic lateral sclerosis (ALS), specifically in motor neurons with abnormal immunoreactive aggregates of phosphorylated TDP-43. These results demonstrate that cellular stressors are key factors in neurodegeneration associated with TDP-43 and disclose the identity of ERK1/2 as novel players in the pathogenesis of ALS.

Emerging drugs for amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disease that results in increasing disability and that is uniformly fatal. Since its approval in the 1990s, riluzole remains the sole treatment for ALS offering modest survival benefit. While significant advances have been made in the symptomatic management of the disease, more effective drug therapy targeting disease progression is sorely needed.

AREAS COVERED

Advances in the understanding of pathogenic mechanisms involved in disease development and progression have provided multiple avenues for developing effective treatment strategies. This review highlights recent discoveries relating to these diverse mechanisms and their implications for the development of drug therapy. Previous human clinical trials that have targeted these pathways are mentioned and ongoing drug trials are discussed.

EXPERT OPINION

The search for effective drug therapy faces important challenges in the areas of basic science and animal research, translation of these results into human clinical trials, inherent bias in human studies and issues related to delays in clinical diagnosis. How these issues may be addressed and why ALS research constitutes fertile grounds for drug development not only for this devastating disease, but also for other more prevalent neurodegenerative diseases, is discussed in this review.

Autoimmunity in amyotrophic lateral sclerosis: past and present

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting particularly motor neurons for which no cure or effective treatment is available. Although the cause of ALS remains unknown, accumulative evidence suggests an autoimmune mechanism of pathogenesis. In this paper, we will summarize the current research related to autoimmunity in the sporadic form of ALS and discuss the potential underlying pathogenic mechanisms and perspectives. Presented data supports the view that humoral immune responses against motor nerve terminals can initiate a series of physiological changes leading to alteration of calcium homeostasis. In turn, loss of calcium homeostasis may induce neuronal death through apoptotic signaling pathways. Additional approaches identifying specific molecular features of this hypothesis are required, which will hopefully allow us to develop techniques of early diagnosis and effective therapies.

Sera from amyotrophic lateral sclerosis patients induce the non-canonical activation of NMDA receptors "in vitro"

Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease characterized by the selective loss of both upper and lower motoneurons (MNs). The familial form of the illness is associated with mutations in the gene encoding Cu/Zn superoxide dismutase 1 (SOD-1) enzyme, but it accounts for fewer than 10% of cases; the rest, more than 90%, correspond to the sporadic form of ALS. Although many proposals have been suggested over the years, the mechanisms underlying the characteristic selective killing of MN in ALS remain unknown. In this study we tested the effect of sera from sporadic ALS patients on NMDA receptors (NMDAR). We hypothesize that an endogenous seric factor is implicated in neuronal death in ALS, mediated by the modulation of NMDAR. Sera from ALS patients and from healthy subjects were pretreated to inactivate complement pathways and dialyzed to remove glutamate and glycine. IgGs from ALS patients and healthy subjects were obtained by affinity chromatography and dialyzed against phosphate-buffered saline. Human NMDAR were expressed in Xenopus laevis oocytes, and ionic currents were recorded using the two-electrode voltage clamp technique. Sera from sporadic ALS patients induced transient oscillatory currents in oocytes expressing NMDAR with a significantly higher total electrical charge than that induced by sera from healthy subjects. Sera from patients with other neuromuscular diseases did not exert this effect. The currents were inhibited by MK-801, a noncompetitive blocker of NMDAR. The PLC inhibitor, U-73122, and the IP(3) receptor antagonist, 2-APB, also inhibited the sera-induced currents. The oscillatory signal recorded was due to internal calcium mobilization. Isolated IgGs from ALS patients significantly affected the activity of oocytes injected with NMDAR, causing a 2-fold increase over the response recorded for IgGs from healthy subjects. Our data support the notion that ALS sera contain soluble factors that mobilize intracellular calcium, not opening directly the ionic conductance, but through the non-canonical activation of NMDAR.

D-serine: the right or wrong isoform?

Only recently, d-amino acids have been identified in mammals. Of these, d-serine has been most extensively studied. d-Serine was found to play an important role as a neurotransmitter in the human central nervous system (CNS) by binding to the N-methyl-d-aspartate receptor (NMDAr), similar to glycine. Therefore, d-serine may well play a role in all physiological and pathological processes in which NMDArs have been implied. In this review, we discuss the findings implying an important role for d-serine in human physiology (CNS development and memory and learning) and pathology (excitotoxicity, perinatal asphyxia, amyotrophic lateral sclerosis (ALS), Alzheimer's disease, epilepsy, schizophrenia and bipolar disorder). We will debate on the relative contribution of d-serine versus glycine and conclude with clinical applications derived from these results and future directions to progress in this field. In general, adequate concentrations of d-serine are required for normal CNS development and function, while both decreased and increased concentrations can lead to CNS pathology. Therefore, d-serine appears to be the right isoform when present in the right concentrations.

Exposure of neurons to excitotoxic levels of glutamate induces cleavage of the RNA editing enzyme, adenosine deaminase acting on RNA 2, and loss of GLUR2 editing

AMPA receptors are glutamate receptors that are tetramers of various combinations of GluR1-4 subunits. AMPA receptors containing GluR1, 3 and 4 are Ca2+ permeable, however, AMPA receptors containing even a single subunit of GluR2 are Ca2+ impermeable. Most AMPA receptors are Ca2+ impermeable due to the presence of GluR2. GluR2 confers special properties on AMPA receptors through the presence of arginine at the pore apex; other subunits (GluR1, 3, 4) contain glutamine at the pore apex and allow Ca2+ influx. Normally, an RNA editing step changes DNA-encoded glutamine to arginine, introduces arginine in the GluR2 pore apex. GluR2 RNA editing is carried out by an RNA-dependent adenosine deaminase (ADAR2). Loss of GluR2 editing leads to the formation of highly excitotoxic AMPA channels [Mahajan and Ziff (2007) Mol Cell Neurosci 35:470-481] and is shown to contribute to loss of motor neurons in amyotrophic lateral sclerosis (ALS). Relatively higher levels of Ca2+-permeable AMPA receptors are found in motor neurons and this has been correlated with lower GluR2 mRNA levels. However, the reason for loss of GluR2 editing is not known. Here we show that exposure of neurons to excitotoxic levels of glutamate leads to specific cleavage of ADAR2 that leads to generation of unedited GluR2. We demonstrate that cleaved ADAR2 leads to a decrease or loss of GluR2 editing, which will further result in high Ca2+ influx and excitotoxic neuronal death.

Disease-related changes in the cerebrospinal fluid metabolome in amyotrophic lateral sclerosis detected by GC/TOFMS

Background/Aim

The changes in the cerebrospinal fluid (CSF) metabolome associated with the fatal neurodegenerative disease amyotrophic lateral sclerosis (ALS) are poorly understood and earlier smaller studies have shown conflicting results. The metabolomic methodology is suitable for screening large cohorts of samples. Global metabolomics can be used for detecting changes of metabolite concentrations in samples of fluids such as CSF.

Methodology

Using gas chromatography coupled to mass spectrometry (GC/TOFMS) and multivariate statistical modeling, we simultaneously studied the metabolome signature of ∼120 small metabolites in the CSF of patients with ALS, stratified according to hereditary disposition and clinical subtypes of ALS in relation to controls.

Principal Findings

The study is the first to report data validated over two sub-sets of ALS vs. control patients for a large set of metabolites analyzed by GC/TOFMS. We find that patients with sporadic amyotrophic lateral sclerosis (SALS) have a heterogeneous metabolite signature in the cerebrospinal fluid, in some patients being almost identical to controls. However, familial amyotrophic lateral sclerosis (FALS) without superoxide dismutase-1 gene (SOD1) mutation is less heterogeneous than SALS. The metabolome of the cerebrospinal fluid of 17 ALS patients with a SOD1 gene mutation was found to form a separate homogeneous group. Analysis of metabolites revealed that glutamate and glutamine were reduced, in particular in patients with a familial predisposition. There are significant differences in the metabolite profile and composition among patients with FALS, SALS and patients carrying a mutation in the SOD1 gene suggesting that the neurodegenerative process in different subtypes of ALS may be partially dissimilar.

Conclusions/Significance

Patients with a genetic predisposition to amyotrophic lateral sclerosis have a more distinct and homogeneous signature than patients with a sporadic disease.

Abnormal exocytotic release of glutamate in a mouse model of amyotrophic lateral sclerosis

Glutamate-mediated excitotoxicity plays a major role in the degeneration of motor neurons in amyotrophic lateral sclerosis and reduced astrocytary glutamate transport, which in turn increases the synaptic availability of the amino acid neurotransmitter, was suggested as a cause. Alternatively, here we report our studies on the exocytotic release of glutamate as a possible source of excessive glutamate transmission. The basal glutamate efflux from spinal cord nerve terminals of mice-expressing human soluble superoxide dismutase (SOD1) with the G93A mutation [SOD1/G93A(+)], a transgenic model of amyotrophic lateral sclerosis, was elevated when compared with transgenic mice expressing the wild-type human SOD1 or to non-transgenic controls. Exposure to 15 mM KCl or 0.3 μM ionomycin provoked Ca(2+)-dependent glutamate release that was dramatically increased in late symptomatic and in pre-symptomatic SOD1/G93A(+) mice. Increased Ca(2+) levels were detected in SOD1/G93A(+) mouse spinal cord nerve terminals, accompanied by increased activation of Ca(2+)/calmodulin-dependent kinase II and increased phosphorylation of synapsin I. In line with these findings, release experiments suggested that the glutamate release augmentation involves the readily releasable pool of vesicles and a greater capability of these vesicles to fuse upon stimulation in SOD1/G93A(+) mice.

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'.

Harmine, a natural beta-carboline alkaloid, upregulates astroglial glutamate transporter expression

Glutamate is the predominant excitatory amino acid neurotransmitter in the mammalian central nervous system (CNS). Glutamate transporter EAAT2/GLT-1 is the physiologically dominant astroglial protein that inactivates synaptic glutamate. Previous studies have shown that EAAT2 dysfunction leads to excessive extracellular glutamate and may contribute to various neurological disorders including amyotrophic lateral sclerosis (ALS). The recent discovery of the neuroprotective properties of ceftriaxone, a beta lactam antibiotic, suggested that increasing EAAT2/GLT-1 gene expression might be beneficial in ALS and other neurological/psychiatric disorders by augmenting astrocytic glutamate uptake. Here we report our efforts to develop a new screening assay for identifying compounds that activate EAAT2 gene expression. We generated fetal derived-human immortalized astroglial cells that are stably expressing a firefly luciferase reporter under the control of the human EAAT2 promoter. When screening a library of 1040 FDA approved compounds and natural products, we identified harmine, a naturally occurring beta-carboline alkaloid, as one of the top hits for activating the EAAT2 promoter. We further tested harmine in our in vitro cell culture systems and confirmed its ability to increase EAAT2/GLT1 gene expression and functional glutamate uptake activity. We next tested its efficacy in both wild type animals and in an ALS animal model of disease and demonstrated that harmine effectively increased GLT-1 protein and glutamate transporter activity in vivo. Our studies provide potential novel neurotherapeutics by modulating the activity of glutamate transporters via gene activation. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

The endocannabinoid system as a target for the treatment of neurodegenerative disease

The Cannabis sativa plant has been exploited for medicinal, agricultural and spiritual purposes in diverse cultures over thousands of years. Cannabis has been used recreationally for its psychotropic properties, while effects such as stimulation of appetite, analgesia and anti-emesis have lead to the medicinal application of cannabis. Indeed, reports of medicinal efficacy of cannabis can been traced back as far as 2700 BC, and even at that time reports also suggested a neuroprotective effect of the cultivar. The discovery of the psychoactive component of cannabis resin, Delta(9)-tetrahydrocannabinol (Delta(9)-THC) occurred long before the serendipitous identification of a G-protein coupled receptor at which Delta(9)-THC is active in the brain. The subsequent finding of endogenous cannabinoid compounds, the synthesis of which is directed by neuronal excitability and which in turn served to regulate that excitability, further widened the range of potential drug targets through which the endocannabinoid system can be manipulated. As a result of this, alterations in the endocannabinoid system have been extensively investigated in a range of neurodegenerative disorders. In this review we examine the evidence implicating the endocannabinoid system in the cause, symptomatology or treatment of neurodegenerative disease. We examine data from human patients and compare and contrast this with evidence from animal models of these diseases. On the basis of this evidence we discuss the likely efficacy of endocannabinoid-based therapies in each disease context.

Astrogliosis in amyotrophic lateral sclerosis: role and therapeutic potential of astrocytes

Amyotrophic lateral sclerosis (ALS) is a fatal disorder characterized by the progressive loss of motor neurons. Although the molecular mechanism underlying motor neuron degeneration remains unknown; non-neuronal cells (including astrocytes) shape motor neuron survival in ALS. Astrocytes closely interact with neurons to provide an optimized environment for neuronal function and respond to all forms of injury in a typical manner known as reactive astrogliosis. A strong reactive astrogliosis surrounds degenerating motor neurons in ALS patients and ALS-animal models. Although reactive astrogliosis in ALS is probably both primary and secondary to motor neuron degeneration; astrocytes are not passive observers and they can influence motor neuron fate. Due to the important functions that astrocytes perform in the central nervous system; it is of key importance to understand how these functions are altered when astrocytes become reactive in ALS. Here; we review the current evidences supporting a potential toxic role of astrocytes and their viability as therapeutic targets to alter motor neuron degeneration in ALS.

Neuroprotective effect of CPDT on THA-induced cortical motor neuron death in an organotypic culture model

Brain stroke, trauma, and motor neuron disease each can result in cortical motoneuron (CMN) death or impairment. Glutamate excitotoxicity induces motor neuron damage in both acute motor neuron loss and chronic motor neuron degeneration. It is necessary to find effective strategies to protect CMNs from excitotoxicity in a variety of pathological conditions. 5,6-Dihydrocyclopenta-1,2-dithiole-3-thione (CPDT) is one of the phase II enzyme inducers. In our previous report, CPDT was shown to have neuroprotective effects on the spinal cord, by activating the Nrf2/ARE pathway to increase antioxidative capacity. In this study, in order to figure out whether CPDT can prevent CMN's from THA-induced death, we set up an organotypic brain slice culture system. Threo-hydroxyaspartate (THA), a glutamate transport inhibitor, was added to the culture medium to induce CMN death by glutamate excitotoxicity. Brain slices were pretreated with CPDT for 48h, then treated with CPDT and THA simultaneously for 3 weeks. We found that pretreatment with CPDT significantly increased CMN survival. Glutamate concentration in the culture medium was significantly greater following THA treatment, whereas no significant decrease was found in the CPDT pretreatment group. However, both Nrf2 and HO-1 protein expression was significantly elevated in the CPDT pretreatment group, and Nrf2 protein translocated to the nucleus after CPDT stimulation. These findings suggest that CPDT can protect CMNs from THA-induced motor neuron death by activating the Nrf2 pathway and increasing HO-1 protein expression. Therefore, increasing antioxidative defense capacity should benefit to upper motor neuron survival following a glutamate excitotoxicity insult.

TNF-α potentiates glutamate-induced spinal cord motoneuron death via NF-κB

Besides glutamate excitotoxicity, the neuroinflammatory response is emerging as a relevant contributor to motoneuron loss in amyotrophic lateral sclerosis (ALS). In this regard, high levels of circulating proinflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) have been shown both in human patients and in animal models of ALS. The aim of this work was to study the effects of TNF-α on glutamate-induced excitotoxicity in spinal cord motoneurons. In rat spinal cord organotypic cultures chronic glutamate excitotoxicity, induced by the glutamate-uptake inhibitor threohydroxyaspartate (THA), resulted in motoneuron loss that was associated with a neuroinflammatory response. In the presence of TNF-α, THA-induced excitotoxic motoneuron death was potentiated. Co-exposure to TNF-α and THA also resulted in down-regulation of the astroglial glutamate transporter 1 (GLT-1) and in increased extracellular glutamate levels, which were prevented by nuclear factor-kappaB (NF-κB) inhibition. Furthermore, TNF-α and THA also cooperated in the induction of oxidative stress in a mechanism involving the NF-κB signalling pathway as well. The inhibition of this pathway abrogated the exacerbation of glutamate-mediated motoneuron death induced by TNF-α. These data link two important pathogenic mechanisms, excitotoxicity and neuroinflammation, suggested to play a role in ALS and, to our knowledge, this is the first time that TNF-α-induced NF-κB activation has been reported to potentiate glutamate excitotoxicity on motononeurons.

Mitochondrial dysfunction and intracellular calcium dysregulation in ALS

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder that affects the aging population. A progressive loss of motor neurons in the spinal cord and brain leads to muscle paralysis and death. As in other common neurodegenerative diseases, aging-related mitochondrial dysfunction is increasingly being considered among the pathogenic factors. Mitochondria are critical for cell survival: they provide energy to the cell, buffer intracellular calcium, and regulate apoptotic cell death. Whether mitochondrial abnormalities are a trigger or a consequence of the neurodegenerative process and the mechanisms whereby mitochondrial dysfunction contributes to disease are not clear yet. Calcium homeostasis is a major function of mitochondria in neurons, and there is ample evidence that intracellular calcium is dysregulated in ALS. The impact of mitochondrial dysfunction on intracellular calcium homeostasis and its role in motor neuron demise are intriguing issues that warrants in depth discussion. Clearly, unraveling the causal relationship between mitochondrial dysfunction, calcium dysregulation, and neuronal death is critical for the understanding of ALS pathogenesis. In this review, we will outline the current knowledge of various aspects of mitochondrial dysfunction in ALS, with a special emphasis on the role of these abnormalities on intracellular calcium handling.

Extracellular ATP and the P2X7 receptor in astrocyte-mediated motor neuron death: implications for amyotrophic lateral sclerosis

Background

During pathology of the nervous system, increased extracellular ATP acts both as a cytotoxic factor and pro-inflammatory mediator through P2X₇ receptors. In animal models of amyotrophic lateral sclerosis (ALS), astrocytes expressing superoxide dismutase 1 (SOD1^G93A) mutations display a neuroinflammatory phenotype and contribute to disease progression and motor neuron death. Here we studied the role of extracellular ATP acting through P2X₇ receptors as an initiator of a neurotoxic phenotype that leads to astrocyte-mediated motor neuron death in non-transgenic and SOD1^G93A astrocytes.

Methods

We evaluated motor neuron survival after co-culture with SOD1^G93A or non-transgenic astrocytes pretreated with agents known to modulate ATP release or P2X₇ receptor. We also characterized astrocyte proliferation and extracellular ATP degradation.

Results

Repeated stimulation by ATP or the P2X₇-selective agonist BzATP caused astrocytes to become neurotoxic, inducing death of motor neurons. Involvement of P2X₇ receptor was further confirmed by Brilliant blue G inhibition of ATP and BzATP effects. In SOD1^G93A astrocyte cultures, pharmacological inhibition of P2X₇ receptor or increased extracellular ATP degradation with the enzyme apyrase was sufficient to completely abolish their toxicity towards motor neurons. SOD1^G93A astrocytes also displayed increased ATP-dependent proliferation and a basal increase in extracellular ATP degradation.

Conclusions

Here we found that P2X₇ receptor activation in spinal cord astrocytes initiated a neurotoxic phenotype that leads to motor neuron death. Remarkably, the neurotoxic phenotype of SOD1^G93A astrocytes depended upon basal activation the P2X₇ receptor. Thus, pharmacological inhibition of P2X₇ receptor might reduce neuroinflammation in ALS through astrocytes.

Riluzole decreases synthesis of N-acetylaspartate and N-acetylaspartylglutamate in SH-SY5Y human neuroblastoma cells

N-acetylaspartate (NAA) is present at very high concentrations in the brain and is used as a non-invasive marker of neuronal viability in magnetic resonance spectroscopy. N-acetylaspartylglutamate (NAAG) is an acetylated dipeptide formed from NAA, and may be an agonist of the mGluR3 receptor. Both NAA and NAAG are synthesized primarily in neurons. Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder resulting in motor neuron death, and progressive paralysis. Levels of both NAA and NAAG are reported to be decreased in ALS. Riluzole is a glutamatergic modulating agent used to treat ALS, but there are conflicting results in the literature concerning the recovery of NAA after riluzole treatment. We studied the effects of riluzole on the biosynthesis of both NAA and NAAG in SH-SY5Y human neuroblastoma cells. We used two methodologies to examine the effect; one involving radiolabel incorporation from corresponding substrates into NAA and NAAG, and the other involving the measurement of endogenous NAA and NAAG levels using HPLC. We show that riluzole treatment, which decreases glutamatergic neuronal excitation, decreases the synthesis and levels of both NAA and NAAG in SH-SY5Y cells in a dose and time dependant manner. These results suggest that the synthesis of NAA and NAAG may be coupled to glutamatergic neurotransmission, and further investigations along these lines are warranted.

Epigallocatechin-3-gallate protects motor neurons and regulates glutamate level

Epigallocatechin-3-gallate (EGCG) is a major component of green tea polyphenols which displays potential properties of anticancer and neuroprotection. Here we show that protection of motor neuron by EGCG is associated with regulating glutamate level in organotypic culture of rat spinal cord. In this model, EGCG blocked glutamate excitotoxicity caused by threohydroxyaspartate, an inhibitor of glutamate transporter. This property of EGCG may be not due to its intrinsic antioxidative activity, because another antioxidant could not regulate glutamate level under the same condition. These results show that EGCG may be a potential therapeutic candidate for neurodegenerative diseases involving glutamate excitotoxicity such as ALS.

Bioanalysis of N-acetyl-aspartyl-glutamate as a marker of glutamate carboxypeptidase II inhibition

We report the characterization of two methods for the analysis of N-acetyl-aspartyl-glutamate (NAAG) in biological fluids. In the first method, NAAG concentrations were calculated based on differences between glutamate concentrations before and after NAAG hydrolysis with exogenous glutamate carboxypeptidase II (GCP II) using high-performance liquid chromatography (HPLC) followed by fluorescence detection. In the second method, NAAG levels were quantified directly using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Analyses of NAAG levels in human cerebrospinal fluid samples using either method gave similar results within experimental error, confirming the validity of the two independent measurements. These methods will be useful in future clinical trials to assess drug-induced GCP II inhibition in biological matrices.

Novel etiological and therapeutic strategies for neurodiseases: RNA editing enzyme abnormality in sporadic amyotrophic lateral sclerosis

The motor neurons of patients with sporadic amyotrophic lateral sclerosis (ALS) express abundant Q/R site-unedited GluR2 mRNA, whereas those of patients with other motor neuron diseases including familial ALS associated with mutated SOD1 (ALS1) and those of normal subjects express only Q/R site-edited GluR2 mRNA. Because adenosine deaminase acting on RNA type 2 (ADAR2) specifically catalyzes GluR2 Q/R site-editing, it is likely that ADAR2 activity is not sufficient to edit this site completely in motor neurons of patients with sporadic ALS. Because these molecular abnormalities occur in disease- and motor neuron-specific fashion and induce fatal epilepsy in mice, we have hypothesized that GluR2 Q/R site-underediting due to ADAR2 underactivity is a cause of neuronal death in sporadic ALS. We found that cytoplasmic fragile X mental retardation protein interacting protein 2 (CYFIP2) mRNA had an ADAR2-mediated editing position using RNA interference knockdown. Our review will include a discussion of new ADAR2 substrates that may be useful for research on sporadic ALS.

AMP kinase-mediated activation of the BH3-only protein Bim couples energy depletion to stress-induced apoptosis

Disturbances in cellular ion gradients by excitotoxicity promote apoptosis through activation of the Bcl-2 family member Bim.

Excitotoxicity after glutamate receptor overactivation induces disturbances in cellular ion gradients, resulting in necrosis or apoptosis. Excitotoxic necrosis is triggered by rapid, irreversible ATP depletion, whereas the ability to recover cellular bioenergetics is suggested to be necessary for the activation of excitotoxic apoptosis. In this study, we demonstrate that even a transient decrease in cellular bioenergetics and an associated activation of adenosine monophosphate–activated protein kinase (AMPK) is necessary for the activation of excitotoxic apoptosis. We show that the Bcl-2 homology domain 3 (BH3)–only protein Bim, a proapoptotic Bcl-2 family member, is activated in multiple excitotoxicity paradigms, mediates excitotoxic apoptosis, and inhibits delayed Ca²⁺ deregulation, mitochondrial depolarization, and apoptosis-inducing factor translocation. We demonstrate that bim activation required the activation of AMPK and that prolonged AMPK activation is sufficient to induce bim gene expression and to trigger a bim-dependent cell death. Collectively, our data demonstrate that AMPK activation and the BH3-only protein Bim couple transient energy depletion to stress-induced neuronal apoptosis.

Oxidative stress in ALS: key role in motor neuron injury and therapeutic target

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterized by death of motor neurons leading to muscle wasting, paralysis, and death, usually within 2-3 years of symptom onset. The causes of ALS are not completely understood, and the neurodegenerative processes involved in disease progression are diverse and complex. There is substantial evidence implicating oxidative stress as a central mechanism by which motor neuron death occurs, including elevated markers of oxidative damage in ALS patient spinal cord and cerebrospinal fluid and mutations in the antioxidant enzyme superoxide dismutase 1 (SOD1) causing approximately 20% of familial ALS cases. However, the precise mechanism(s) by which mutant SOD1 leads to motor neuron degeneration has not been defined with certainty, and the ultimate trigger for increased oxidative stress in non-SOD1 cases remains unclear. Although some antioxidants have shown potential beneficial effects in animal models, human clinical trials of antioxidant therapies have so far been disappointing. Here, the evidence implicating oxidative stress in ALS pathogenesis is reviewed, along with how oxidative damage triggers or exacerbates other neurodegenerative processes, and we review the trials of a variety of antioxidants as potential therapies for ALS.

In vitro neurotoxic properties and excitatory aminoacids concentration in the cerebrospinal fluid of amyotrophic lateral sclerosis patients. Relationship with the degree of certainty of disease diagnoses

OBJECTIVE

To determine glutamate and aspartate levels in the cerebrospinal fluid (CSF) in patients with sporadic amyotrophic lateral sclerosis (SALS) grouped according to El Escorial diagnostic criteria, and to perform an in vitro assessment of the neurotoxicity of the CSF in murine cortical neurons.

METHODS

SALS patients were sorted according to El Escorial diagnostic criteria. Glutamate and aspartate were measured in the CSF using high performance liquid chromatography. Cultured cortical neuron viability was determined after exposure to CSF for 24 h.

RESULTS

Glutamate levels were elevated in 28 out of the 29 patients with definite, probable or possible SALS. There were no differences in glutamate concentrations when the three clinical forms of the disease were compared; neither there were significant variation across disease duration and clinical presentation. In agreement with previous reports, we concluded that CSF-SALS-induced in vitro neurotoxicity is mediated by ionotropic glutamate receptors. We found no relationship between the degree of in vitro neurotoxicity and glutamate concentration in the CSF.

CONCLUSIONS

Glutamate but not aspartate CSF levels may contribute to ALS pathogenesis. However, glutamate levels may not influence the degree of diagnosis certainty or lesion extension.

Amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a common neurological disorder that results in loss of motor neurons, leading to a rapidly progressive form of muscle paralysis that is fatal. There is no available cure and current therapies only provide minimal benefit at best. The disease is predominantly sporadic and until very recently only the Cu,Zn superoxide dismutase (Cu,ZnSOD), which is involved in a small number of sporadic cases and a larger component of familial ones, have been analyzed in any detail. Here we describe the clinical aspects of ALS and highlight the genetics and molecular mechanisms behind the disease. We discuss the current understanding and controversies of how mutations in Cu,ZnSOD may cause the disease. We also focus on the recent discovery that mutations in either TDP-43 or FUS/TLS, which are both involved in DNA/RNA synthesis, are likely the cause behind many cases of ALS that are not linked to Cu,ZnSOD.

Transgenic expression of Glud1 (glutamate dehydrogenase 1) in neurons: in vivo model of enhanced glutamate release, altered synaptic plasticity, and selective neuronal vulnerability

The effects of lifelong, moderate excess release of glutamate (Glu) in the CNS have not been previously characterized. We created a transgenic (Tg) mouse model of lifelong excess synaptic Glu release in the CNS by introducing the gene for glutamate dehydrogenase 1 (Glud1) under the control of the neuron-specific enolase promoter. Glud1 is, potentially, an important enzyme in the pathway of Glu synthesis in nerve terminals. Increased levels of GLUD protein and activity in CNS neurons of hemizygous Tg mice were associated with increases in the in vivo release of Glu after neuronal depolarization in striatum and in the frequency and amplitude of miniature EPSCs in the CA1 region of the hippocampus. Despite overexpression of Glud1 in all neurons of the CNS, the Tg mice suffered neuronal losses in select brain regions (e.g., the CA1 but not the CA3 region). In vulnerable regions, Tg mice had decreases in MAP2A labeling of dendrites and in synaptophysin labeling of presynaptic terminals; the decreases in neuronal numbers and dendrite and presynaptic terminal labeling increased with advancing age. In addition, the Tg mice exhibited decreases in long-term potentiation of synaptic activity and in spine density in dendrites of CA1 neurons. Behaviorally, the Tg mice were significantly more resistant than wild-type mice to induction and duration of anesthesia produced by anesthetics that suppress Glu neurotransmission. The Glud1 mouse might be a useful model for the effects of lifelong excess synaptic Glu release on CNS neurons and for age-associated neurodegenerative processes.

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.