Cytokine upregulation in a murine model of familial amyotrophic lateral sclerosis

Motor neuron trophic factors: therapeutic use in ALS?

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

Glial cells in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult motor neuron disease characterized by premature death of upper and lower motor neurons. Two percent of ALS cases are caused by the dominant mutations in the gene for superoxide dismutase 1 (SOD1) through a gain of toxic property of mutant protein. Genetic and chimeric mice studies using SOD1 models indicate that non-neuronal cells play important roles in neurodegeneration through non-cell autonomous mechanism. We review the contribution of each glial cell type in ALS pathology from studies of the rodent models and ALS patients. Astrogliosis and microgliosis are not only considerable hallmarks of the disease, but the intensity of microglial activation is correlated with severity of motor neuron damage in human ALS. The impaired astrocytic functions such as clearance of extracellular glutamate and release of neurotrophic factors are implicated in disease. Further, the damage within astrocytes and microglia is involved in accelerated disease progression. Finally, other glial cells such as NG2 cells, oligodendrocytes and Schwann cells are under the investigation to determine their contribution in ALS. Accumulating knowledge of active role of glial cells in the disease should be carefully applied to understanding of the sporadic ALS and development of therapy targeted for glial cells.

Targeting TNF-α to elucidate and ameliorate neuroinflammation in neurodegenerative diseases

Inflammatory signals generated within the brain and peripheral nervous system direct diverse biological processes. Key amongst the inflammatory molecules is tumor necrosis factor-α (TNF-α), a potent pro-inflammatory cytokine that, via binding to its associated receptors, is considered to be a master regulator of cellular cascades that control a number of diverse processes coupled to cell viability, gene expression, synaptic integrity and ion homeostasis. Whereas a self-limiting neuroinflammatory response generally results in the resolution of an intrinsically or extrinsically triggered insult by the elimination of toxic material or injured tissue to restore brain homeostasis and function, in the event of an unregulated reaction, where the immune response persists, inappropriate chronic neuroinflammation can ensue. Uncontrolled neuroinflammatory activity can induce cellular dysfunction and demise, and lead to a self-propagating cascade of harmful pathogenic events. Such chronic neuroinflammation is a typical feature across a range of debilitating common neurodegenerative diseases, epitomized by Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis, in which TNF-α expression appears to be upregulated and may represent a valuable target for intervention. Elaboration of the protective homeostasis signaling cascades from the harmful pathogenic ones that likely drive disease onset and progression could aid in the clinical translation of approaches to lower brain and peripheral nervous system TNF-α levels, and amelioration of inappropriate neuroinflammation.

Neuroinflammation in amyotrophic lateral sclerosis: role of glial activation in motor neuron disease

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS) are characterised by the appearance of reactive microglial and astroglial cells, a process referred to as neuroinflammation. In transgenic mouse models of mutant SOD1-associated familial ALS, reactive microglial cells and astrocytes actively contribute to the death of motor neurons. The biological processes that drive this glial reaction are complex and have both beneficial and deleterious effects on motor neurons. Therapeutic interventions targeting these cells are being explored. An improved understanding of the biological processes that cause neuroinflammation will help to define its medical importance and to identify the therapeutic potential of interfering with this reaction.

Activation of interferon signaling pathways in spinal cord astrocytes from an ALS mouse model

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder affecting predominantly motor neurons. Recent studies suggest that the disease progression of ALS is non-cell-autonomous, although the interaction between neurons and glial cells in different disease stages is not entirely clear. Here, we demonstrate that the interferon (IFN) signaling pathway is activated in human SOD1(G93A) transgenic mice, a rodent model of ALS. IFN-stimulated genes (ISGs) increased in the spinal cord of SOD1(G93A) mice at a presymptomatic age. In addition, the up-regulated ISGs, and most likely their transcriptional activators, were found specifically in astrocytes surrounding motor neurons, suggesting that IFN signaling in astrocytes was triggered by specific pathologic changes in motor neurons. Furthermore, induction of ISGs in cultured astrocytes was highly sensitive to IFN, especially Type I IFN. ISGs in astrocytes were activated specifically by endoplasmic reticulum stress-induced neurodegeneration in vitro, implicating a similar process in the presymptomatic stage of SOD1 mutant mice. Finally, reduction or deletion of IFNα receptor 1 inhibited IFN signaling and increased the life-span of SOD1(G93A) mice. Thus, the activation of IFN signaling pathways represents an early "dialogue" between motor neurons and astrocytes in response to pathological changes in ALS.

IL-17A is increased in the serum and in spinal cord CD8 and mast cells of ALS patients

The contribution of inflammation to neurodegenerative diseases is increasingly recognized, but the role of inflammation in sporadic amyotrophic lateral sclerosis (sALS) is not well understood and no animal model is available. We used enzyme-linked immunosorbent assays (ELISAs) to measure the cytokine interleukin-17A (IL-17A) in the serum of ALS patients (n = 32; 28 sporadic ALS (sALS) and 4 familial ALS (fALS)) and control subjects (n = 14; 10 healthy subjects and 4 with autoimmune disorders). IL-17A serum concentrations were 5767 ± 2700 pg/ml (mean ± SEM) in sALS patients and 937 ± 927 pg/ml in fALS patients in comparison to 7 ± 2 pg/ml in control subjects without autoimmune disorders (p = 0.008 ALS patients vs. control subjects by Mann-Whitney test). Sixty-four percent of patients and no control subjects had IL-17A serum concentrations > 50 pg/ml (p = 0.003 ALS patients vs. healthy subjects by Fisher's exact test). The spinal cords of sALS (n = 8), but not control subjects (n = 4), were infiltrated by interleukin-1β- (IL-1β-), and tumor necrosis factor-α-positive macrophages (co-localizing with neurons), IL-17A-positive CD8 cells, and IL-17A-positive mast cells. Mononuclear cells treated with aggregated forms of wild type superoxide dismutase-1 (SOD-1) showed induction of the cytokines IL-1β, interleukin-6 (IL-6), and interleukin-23 (IL-23) that may be responsible for induction of IL-17A. In a microarray analysis of 28,869 genes, stimulation of peripheral blood mononuclear cells by mutant superoxide dismutase-1 induced four-fold higher transcripts of interleukin-1α (IL-1α), IL-6, CCL20, matrix metallopeptidase 1, and tissue factor pathway inhibitor 2 in mononuclear cells of patients as compared to controls, whereas the anti-inflammatory cytokine interleukin-10 (IL-10) was increased in mononuclear cells of control subjects. Aggregated wild type SOD-1 in sALS neurons could induce in mononuclear cells the cytokines inducing chronic inflammation in sALS spinal cord, in particular IL-6 and IL-17A, damaging neurons. Immune modulation of chronic inflammation may be a new approach to sALS.

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.

Microglia in ALS: the good, the bad, and the resting

Inflammation, including microglial activation and T cell infiltration, is a neuropathological hallmark of amyotrophic lateral sclerosis (ALS), a rapidly progressing neurodegenerative disease. The identification of mutations in the gene for Cu2+/Zn2+ superoxide dismutase (SOD1) from patients with an inherited form of ALS enabled the creation of transgenic mice overexpressing mutant forms of SOD1 (mSOD1) which develop a motoneuron disease that resembles the disease seen in ALS patients. These transgenic mice display similar inflammatory reactions at sites of motoneuron injury as detected in ALS patients, enabling the observation that this inflammation is not simply a late consequence of motoneuron degeneration, but actively contributes to the balance between neuroprotection and neurotoxicity. The microglial and T cell activation states influence the rate of disease progression. Initially, microglia and T cells can slow disease progression, while they may later contribute to the acceleration of disease. Accumulation of intracellular and extracellular misfolded mSOD1 may be key events regulating the transformation from neuroprotective alternatively activated M2 microglia to cytotoxic classically activated M1 microglia. Intracellular and extracellular mSOD1 utilizing different pathways may enhance the production and release of reactive oxygen species (ROS) and augment the inflammatory cytokine cascade from microglia. These ROS and cytokines may increase the susceptibility of motoneurons to glutamate toxicity and inhibit the function and expression of astrocytic glutamate transporters resulting in further neurotoxicity. Thus, the cumulative evidence suggests that inflammation plays a central role in ALS and manipulating these microglial effector functions may potentially modify the outcome of this devastating disease.

Motor neuron-immune interactions: the vicious circle of ALS

Because microglial cells, the resident macrophages of the CNS, react to any lesion of the nervous system, they have for long been regarded as potential players in the pathogenesis of several neurodegenerative disorders including amyotrophic lateral sclerosis, the most common motor neuron disease in the adult. In recent years, this microglial reaction to motor neuron injury, in particular, and the innate immune response, in general, has been implicated in the progression of the disease, in mouse models of ALS. The mechanisms by which microglial cells influence motor neuron death in ALS are still largely unknown. Microglial activation increases over the course of the disease and is associated with an alteration in the production of toxic factors and also neurotrophic factors. Adding to the microglial/macrophage response to motor neuron degeneration, the adaptive immune system can likewise influence the disease process. Exploring these motor neuron-immune interactions could lead to a better understanding in the physiopathology of ALS to find new pathways to slow down motor neuron degeneration.

Distinct biochemical signatures characterize peripherin isoform expression in both traumatic neuronal injury and motor neuron disease

Peripherin is a type III intermediate filament protein that is up-regulated during neuronal injury and is a major component of pathological inclusions found within degenerating motor neurons of patients with amyotrophic lateral sclerosis (ALS). The relationship between these inclusions and their protein constituents remains largely unknown. We have previously shown that peripherin expression is characterized by tissue-specific, intra-isoform associations that contribute to filament structure; changes to the normal isoform expression pattern is associated with malformed filaments and intracellular inclusions. Here, we profile peripherin isoform expression and ratio changes in traumatic neuronal injury, transgenic mouse models of motor neuron disease, and ALS. Extensive western blot analyses of Triton X-100 soluble and insoluble fractions of neuronal tissue from these conditions revealed significant changes in peripherin isoform content which could be differentiated by electrophoretic banding patterns to produce distinct peripherin biochemical signatures. Significantly, we found that the pattern of peripherin expression in ALS most closely approximates that of peripherin over-expressing mice, but differs with regard to inter-individual variations in isoform-specific expression. Overall, these results provide important insights into complex post-transcriptional processes that may underlie a continuum between peripherin-mediated neuronal repair and its role in the pathogenesis of motor neuron disease.

Reduction of circulating endothelial cells in peripheral blood of ALS patients

Background

Amyotrophic Lateral Sclerosis (ALS) treatment is complicated by the various mechanisms underlying motor neuron degeneration. Recent studies showed that the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB) are compromised in an animal model of ALS due to endothelial cell degeneration. A later study demonstrated a loss of endothelium integrity in the spinal cords of ALS patients. Since circulating endothelial cells (CECs) in the peripheral blood are associated with endothelium damage, being detached dysfunctional endothelial cells, we hypothesized that CEC levels may reflect endothelium condition in ALS patients.

Methodology/Principal Findings

CEC levels were estimated in whole blood smears from ALS patients with moderate stage (_MALS), severe stage (_SALS), and healthy controls by CD146 expression using immunocytochemistry. A significant reduction of CECs was detected in _MALS and _SALS patients.

Conclusions/Significance

CECs did not predict endothelium state in ALS patients; however, endothelial damage and/or impaired endothelium repair may occur in ALS leading to BBB/BSCB dysfunction. Reduced CECs in peripheral blood of ALS patients may indicate different mechanisms of endothelial damage and repair, rather than only detachment of dysfunctional endothelial cells. Although a potential mechanism of CEC reduction is discussed, establishing a reliable indicator of endothelial dysfunction/damage is important for evaluation of BBB/BSCB status in ALS patients during disease progression.

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.

Efficacy of thalidomide for the treatment of amyotrophic lateral sclerosis: a phase II open label clinical trial

Neuroinflammation through the cytokine, tumor necrosis factor-alpha (TNF-alpha) is thought to play an important role in the pathogenesis of amyotrophic lateral sclerosis (ALS). We conducted a preliminary phase II trial of thalidomide, which reduces levels of TNF-alpha pre-transcriptionally and post-transcriptionally in vivo and has been shown to prolong disease duration and extend the lifespan of transgenic animal models of ALS. Patients who met diagnostic criteria for ALS received thalidomide at escalating doses to a target dose of 400 mg/day. The primary endpoints in the trial were the ALS Functional Rating Scale (ALSFRS) and pulmonary function testing (PFT) curves after nine months of thalidomide treatment that were compared to historical controls. Secondary endpoints were: survival stratified for newly diagnosed and progressive disease, toxicity, quality of life, and serum cytokine measurements. Twenty-three patients were enrolled, but only 18 were evaluable for the primary outcome. There was no improvement in the ALSFRS or PFT compared to historical controls. Thalidomide had several side-effects in our ALS patients. There was no significant shift in cytokine profile after treatment compared to baseline. In conclusion, treatment of ALS with the TNF-alpha inhibitor, thalidomide, does not appear to effectively modulate disease progression and can cause adverse effects.

Does neuroinflammation fan the flame in neurodegenerative diseases?

While peripheral immune access to the central nervous system (CNS) is restricted and tightly controlled, the CNS is capable of dynamic immune and inflammatory responses to a variety of insults. Infections, trauma, stroke, toxins and other stimuli are capable of producing an immediate and short lived activation of the innate immune system within the CNS. This acute neuroinflammatory response includes activation of the resident immune cells (microglia) resulting in a phagocytic phenotype and the release of inflammatory mediators such as cytokines and chemokines. While an acute insult may trigger oxidative and nitrosative stress, it is typically short-lived and unlikely to be detrimental to long-term neuronal survival. In contrast, chronic neuroinflammation is a long-standing and often self-perpetuating neuroinflammatory response that persists long after an initial injury or insult. Chronic neuroinflammation includes not only long-standing activation of microglia and subsequent sustained release of inflammatory mediators, but also the resulting increased oxidative and nitrosative stress. The sustained release of inflammatory mediators works to perpetuate the inflammatory cycle, activating additional microglia, promoting their proliferation, and resulting in further release of inflammatory factors. Neurodegenerative CNS disorders, including multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), tauopathies, and age-related macular degeneration (ARMD), are associated with chronic neuroinflammation and elevated levels of several cytokines. Here we review the hallmarks of acute and chronic inflammatory responses in the CNS, the reasons why microglial activation represents a convergence point for diverse stimuli that may promote or compromise neuronal survival, and the epidemiologic, pharmacologic and genetic evidence implicating neuroinflammation in the pathophysiology of several neurodegenerative diseases.

Inflammation in ALS and SMA: sorting out the good from the evil

Indices of neuroinflammation are found in a variety of diseases of the CNS including amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). Over the years, neuroinflammation, in degenerative disorders of the CNS, has evolved from being regarded as an innocent bystander accomplishing its housekeeping function secondary to neurodegeneration to being considered as a bona fide contributor to the disease process and, in some situations, as a putative initiator of the disease. Herein, we will review neuroinflammation in both ALS and SMA not only from the angle of neuropathology but also from the angle of its potential role in the pathogenesis and treatment of these two dreadful paralytic disorders.

Inflammation in amyotrophic lateral sclerosis spinal cord and brain is mediated by activated macrophages, mast cells and T cells

Recent studies have shown inflammatory markers in affected neural tissues of amyotrophic lateral sclerosis (ALS) patients. We examined immunocytochemically spinal cord tissues of six patients with ALS, two with corticospinal tract degeneration secondary to cerebral infarcts and three control subjects without neuropathologic abnormalities. ALS spinal cords had dense macrophage infiltration (one log greater than control spinal cords) involving the white and gray matter, with heaviest infiltration of lateral and ventral columns and, in one patient, prefrontal gyrus and the occipital lobes of the brain. Macrophages in ALS spinal cord showed strong expression of cyclooxygenase-2 (COX-2) (one log greater than control tissues) and inducible nitric oxide synthase. In the gray matter, macrophages surrounded and appeared to phagocytize neurons (NeuN-positive) that appeared to be dying. Vessels showed damage to the tight junction protein ZO-1 in relation to perivascular CD40 receptor-positive macrophages and CD40 ligand-positive T lymphocytes. ALS spinal cords, but not control cords, were sparsely infiltrated with mast cells. In control cases with corticospinal tract degeneration following hemispheric cerebral infarction, macrophage infiltration of the white matter was COX-2-negative and restricted to lateral and anterior corticospinal tracts. Our data suggest that inflammation in ALS spinal cord and cortex is based on innate immune responses by macrophages and mast cells and adaptive immune responses by T cells.

Development of immunization approaches to amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by loss of motor neurons in the brain and spinal cord. Mutations in the gene encoding superoxide dismutase (SOD1) remain the major known genetic causes associated with ALS. Evidence suggests that the toxicity of SOD1 mutations is related to the abnormal misfolding and aggregation of mutant SOD1 proteins. The discovery of a secretion pathway for mutant SOD1 increased the possibility of using immunization approaches to reduce or neutralize the burden of toxic SOD1 species in the nervous system. Both active and passive immunization protocols were successful in delaying the onset of disease and mortality in transgenic mice expressing mutant SOD1. Owing to the potential adverse immune responses, immunization strategies need to be considered cautiously before being tested in human clinical trials. Critical issues for development of human immunotherapy will be discussed including the routes and methods of antibody delivery, the specificity of antibodies and immune responses, the penetration through the BBB and the time to start treatment. Prophylactic immunotherapy may become a conceivable approach for SOD1-linked ALS patients providing that the treatment is not overly invasive and can be implemented at reasonable cost. This article reviews how innate and adaptive immunity can affect the pathogenesis of ALS and how harnessing the immune system through immunization approaches might offer promising future therapeutic avenues.

Tumor necrosis factor alpha and interferon gamma cooperatively induce oxidative stress and motoneuron death in rat spinal cord embryonic explants

The accumulation of reactive microglia in the degenerating areas of amyotrophic lateral sclerosis (ALS) tissue is a key cellular event creating a chronic inflammatory environment that results in motoneuron death. We have developed a new culture system that consists in rat spinal cord embryonic explants in which motoneurons migrate outside the explant, growing as a monolayer in the presence of glial cells. The proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) have been proposed to be involved in ALS-linked microglial activation. In our explants, the combined exposure to these cytokines resulted in an increased expression of the pro-oxidative enzymes inducible nitric oxide synthase (iNOS), the catalytic subunit of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, gp91(phox) and cyclooxygenase-2 (COX-2), as compared to each cytokine alone. This effect was related to their cooperation in the activation of the transcription factor nuclear factor kappa B (NF-kappaB). TNF-alpha and IFN-gamma also cooperated to promote protein oxidation and nitration, thus increasing the percentage of motoneurons immunoreactive for nitrotyrosine. Apoptotic motoneuron death, measured through annexin V-Cy3 and active caspase-3 immunoreactivities, was also found cooperatively induced by TNF-alpha and IFN-gamma. Interestingly, these cytokines did not affect the viability of purified spinal cord motoneurons in the absence of glial cells. It is proposed that the proinflammatory cytokines TNF-alpha and IFN-gamma have cooperative/complementary roles in inflammation-induced motoneuron death.

The complement factor C5a receptor is upregulated in NFL-/- mouse motor neurons

In NFL-/- mice, a model of motor neuron degeneration in ALS, degenerating spinal motor neurons express high levels of the receptor for the C5a anaphylatoxin (C5aR) early in the disease process. C5a is a potent in vitro neurotoxin for both Neuro2A and NGF-differentiated PC12 cells. While no interaction was observed between glutamate and C5a, both C5a and kainate upregulated the expression of activated C5aR. C5aR expression was increased in motor neurons in ALS. This data suggests that the early upregulation of C5aR may contribute to motor neuron damage that potentiates excitotoxicity in ALS.

Dysregulation of iron homeostasis in the CNS contributes to disease progression in a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), characterized by degeneration of spinal motor neurons, consists of sporadic and familial forms. One cause of familial ALS is missense mutations in the superoxide dismutase 1 (SOD1) gene. Iron accumulation occurs in the CNS of both forms of ALS; however, its contribution to the pathogenesis of ALS is not known. We examined the role of iron in a transgenic mouse line overexpressing the human SOD1(G37R) mutant. We show that multiple mechanisms may underlie the iron accumulation in neurons and glia in SOD1(G37R) transgenic mice. These include dysregulation of proteins involved in iron influx and sensing of intracellular iron; iron accumulation in ventral motor neurons secondary to blockage of anterograde axonal transport; and increased mitochondrial iron load in neurons and glia. We also show that treatment of SOD1(G37R) mice with an iron chelator extends life span by 5 weeks, accompanied by increased survival of spinal motor neurons and improved locomotor function. These data suggest that iron chelator therapy might be useful for the treatment of ALS.

Motor impairment and aberrant production of neurochemicals in human alpha-synuclein A30P+A53T transgenic mice with alpha-synuclein pathology

Missense point mutations, duplication and triplication in the alpha-synuclein (alphaSYN) gene have been identified in familial Parkinson's disease (PD). Familial and sporadic PD show common pathological features of alphaSYN pathologies, e.g., Lewy bodies (LBs) and Lewy neurites (LNs), and a loss of dopaminergic neurons in the substantia nigra that leads to motor disturbances. To elucidate the mechanism of alphaSYN pathologies, we generated TgalphaSYN transgenic mice overexpressing human alphaSYN with double mutations in A30P and A53T. Human alphaSYN accumulated widely in neurons, processes and aberrant neuronal inclusion bodies. Sarcosyl-insoluble alphaSYN, as well as phosphorylated, ubiquitinated and nitrated alphaSYN, was accumulated in the brains. Significantly decreased levels of dopamine (DA) were recognized in the striatum. Motor impairment was revealed in a rotarod test. Thus, TgalphaSYN is a useful model for analyzing the pathological cascade from aggregated alphaSYN to motor disturbance, and may be useful for drug trials.

Skeletal muscle is a primary target of SOD1G93A-mediated toxicity

The antioxidant enzyme superoxide dismutase 1 (SOD1) is a critical player of the antioxidative defense whose activity is altered in several chronic diseases, including amyotrophic lateral sclerosis. However, how oxidative insult affects muscle homeostasis remains unclear. This study addresses the role of oxidative stress on muscle homeostasis and function by the generation of a transgenic mouse model expressing a mutant SOD1 gene (SOD1(G93A)) selectively in skeletal muscle. Transgenic mice developed progressive muscle atrophy, associated with a significant reduction in muscle strength, alterations in the contractile apparatus, and mitochondrial dysfunction. The analysis of molecular pathways associated with muscle atrophy revealed that accumulation of oxidative stress served as signaling molecules to initiate autophagy, one of the major intracellular degradation mechanisms. These data demonstrate that skeletal muscle is a primary target of SOD1(G93A) -mediated toxicity and disclose the molecular mechanism whereby oxidative stress triggers muscle atrophy.

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

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

Glial cells in ALS: the missing link?

Amyotrophic lateral sclerosis (ALS) was initially known as Charcot's sclerosis, named after the French neurobiologist and physician Jean-Martin Charcot who first described this type of muscular atrophy in the early nineteenth century. In the United States, ALS became widely known as Lou Gehrig's disease after the famous baseball player who succumbed to the disease in the late 1930s. Currently, ALS is the most common motor neuron disease, with a worldwide incidence of 8 cases per 100,000 population per year. Familial forms constitute approximately 5% to 10% of all cases. Onset increases with age, with a peak in the seventh decade and a slight preponderance (relative risk, 1.3-1.5) among men compared with women. Rapid progression of motor neuron loss leads to death an average of 3 to 5 years after symptom onset. The cause of ALS remains unknown and there is still no curative therapy.

Inflammatory cytokines increase mitochondrial damage in motoneuronal cells expressing mutant SOD1

Recent studies indicate that molecular signals from microglia determine disease progression in transgenic mice overexpressing mutant superoxide dismutase (mutSOD1) typical of amyotrophic lateral sclerosis patients and that toxicity of mutSOD1 in motor neurons descends from its tendency to associate with mitochondria. To assess whether the neurotoxicity of mutSOD1 is influenced by signals from glia, we challenged motoneuronal cells overexpressing either wild-type or mutant SOD1 with inflammatory cytokines. We have obtained evidence that combined treatment with tumor necrosis factor alpha and interferon gamma increases the fraction of both wtSOD1 and mutSOD1 associated with mitochondria, but these inflammatory cytokines dramatically alter morphological features and functionality of mitochondria only in cells expressing mutSOD1. As an effect downstream the increase in mitochondria-associated mutSOD1, the ratio between reduced and oxidized glutathione further shifts toward the oxidized form in this compartment and a clear death phenotype is evoked upon treatment with inflammatory cytokines. These results suggest that signals coming from non-neuronal cells contribute to death of motor neurons induced by mutSOD1 through reinforcement of mitochondrial damage.

Adaptive immune neuroprotection in G93A-SOD1 amyotrophic lateral sclerosis mice

Background

Innate neuroimmune dysfunction is a pathobiological feature of amyotrophic lateral sclerosis (ALS). However, links, if any, between disease and adaptive immunity are poorly understood. Thus, the role of T cell immunity in disease was investigated in human G93A superoxide dismutase 1 (SOD1) transgenic (Tg) mice and subsequently in ALS patients.

Methods and Findings

Quantitative and qualitative immune deficits in lymphoid cell and T cell function were seen in G93A-SOD1 Tg mice. Spleens of Tg animals showed reductions in size, weight, lymphocyte numbers, and morphological deficits at terminal stages of disease compared to their wild-type (Wt) littermates. Spleen sizes and weights of pre-symptomatic Tg mice were unchanged, but deficits were readily seen in T cell proliferation coincident with increased annexin-V associated apoptosis and necrosis of lymphocytes. These lymphoid deficits paralleled failure of Copolymer-1 (COP-1) immunization to affect longevity. In addition, among CD4⁺ T cells in ALS patients, levels of CD45RA⁺ (naïve) T cells were diminished, while CD45RO⁺ (memory) T cells were increased compared to age-matched caregivers. In attempts to correct mutant SOD1 associated immune deficits, we reconstituted SOD1 Tg mice with unfractionated naïve lymphocytes or anti-CD3 activated CD4⁺CD25⁺ T regulatory cells (Treg) or CD4⁺CD25⁻ T effector cells (Teff) from Wt donor mice. While naive lymphocytes failed to enhance survival, both polyclonal-activated Treg and Teff subsets delayed loss of motor function and extended survival; however, only Treg delayed neurological symptom onset, whereas Teff increased latency between disease onset and entry into late stage.

Conclusions

A profound and progressive immunodeficiency is operative in G93A-SOD1 mice and is linked to T cell dysfunction and the failure to elicit COP-1 neuroprotective immune responses. In preliminary studies T cell deficits were also observed in human ALS. These findings, taken together, suggest caution in ascribing vaccination outcomes when these animal models of human ALS are used for study. Nonetheless, the abilities to improve neurological function and life expectancy in G93A-SOD1 Tg mice by reconstitution with activated T cells do provide opportunities for therapeutic intervention.

Human umbilical cord blood treatment in a mouse model of ALS: optimization of cell dose

Background

Amyotrophic Lateral Sclerosis (ALS) is a multicausal disease characterized by motor neuron degeneration in the spinal cord and brain. Cell therapy may be a promising new treatment for this devastating disorder. We recently showed that a single low dose (10⁶ cells) of mononuclear human umbilical cord blood (MNC hUCB) cells administered intravenously to G93A mice delayed symptom progression and modestly prolonged lifespan. The aim of this pre-clinical translation study is to optimize the dose of MNC hUCB cells to retard disease progression in G93A mice. Three different doses of MNC hUCB cells, 10×10⁶, 25×10⁶ and 50×10⁶, were administered intravenously into pre-symptomatic G93A mice. Motor function tests and various assays to determine cell effects were performed on these mice.

Methodology/Principal Findings

Our results showed that a cell dose of 25×10⁶ cells significantly increased lifespan of mice by 20–25% and delayed disease progression by 15%. The most beneficial effect on decreasing pro-inflammatory cytokines in the brain and spinal cord was found in this group of mice. Human Th2 cytokines were found in plasma of mice receiving 25×10⁶ cells, although prevalent human Th1 cytokines were indicated in mice with 50×10⁶ cells. High response of splenic cells to mitogen (PHA) was indicated in mice receiving 25×10⁶ (mainly) and 10×10⁶ cells. Significantly increased lymphocytes and decreased neutrophils in the peripheral blood were found only in animals receiving 25×10⁶ cells. Stable reduction in microglia density in both cervical and lumbar spinal cords was also noted in mice administered with 25×10⁶ cells.

Conclusions/Significance

These results demonstrate that treatment for ALS with an appropriate dose of MNC hUCB cells may provide a neuroprotective effect for motor neurons through active involvement of these cells in modulating the host immune inflammatory system response.

Adult glial precursor proliferation in mutant SOD1G93A mice

The focus of most neurodegenerative disease studies has been on neuronal death in particular subpopulations of the central nervous system. The associated response of glial populations has been ascribed the term "reactive astrocytosis." This has been defined as the proliferation of astrocytes accompanied by cellular hypertrophy and changes in gene expression following injury to the central nervous system. Yet the significance of that response to disease course is debated. In both human ALS and in the SOD1G93A mouse model of ALS, reactive astrocytosis is a hallmark of the disease--particularly at endstage. The brain also harbors immature progenitors which have the capacity for differentiation into both glial and neuronal lineages. We examined whether glial progenitors in the adult spinal cord of SOD1G93A mice become activated and contribute the astroglial response observed in this model. We found that the glial progenitor proteoglycan NG2 is increased in parallel with GFAP during the symptomatic phase of the disease and that there is a differential in vitro response of SOD1G93A glial progenitors to inflammatory cytokines when compared to wildtype mouse glial progenitors. This response was accompanied by the proliferation of glial progenitors but not mature GFAP+ astrocytes, through the translocation of the transcription factor Olig2 from the nucleus to the cytoplasm-resulting in astrocyte differentiation. These data suggest that adult glial progenitors from SOD1G93A mice differentially respond to inflammatory cytokines and contribute to the observed reactive astrocytosis observed in SOD1G93A mouse lumbar spinal cord.

Amyotrophic lateral sclerosis: from current developments in the laboratory to clinical implications

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive degeneration of motor neurons occurring both as a sporadic and a familial disease. The etiology of ALS remains unknown, but one fifth of instances are due to specific gene defects, the best characterized of which is point mutations in the gene coding for Cu/Zn superoxide dismutase (SOD1). Because sporadic and familial ALS affect the same neurons with similar pathology, it is hoped that understanding these gene defects will help in devising therapies effective in both forms. A wealth of evidence has been collected in rodents made transgenic for mutant SOD1, which represent the best available models for familial ALS. Mutant SOD1 likely induces selective vulnerability of motor neurons through a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, cytoskeletal abnormalities and defective axonal transport, excitotoxicity, inadequate growth factor signaling, and inflammation. Damage within motor neurons is enhanced by noxious signals originating from nonneuronal neighboring cells, where mutant SOD1 induces an inflammatory response that accelerates disease progression. The clinical implication of these findings is that promising therapeutic approaches can be derived from multidrug treatments aimed at the simultaneous interception of damage in both motor neurons and nonmotor neuronal cells.

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

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

Mutant Cu/Zn-superoxide dismutase associated with amyotrophic lateral sclerosis destabilizes vascular endothelial growth factor mRNA and downregulates its expression

Vascular endothelial growth factor (VEGF) plays a neuroprotective role in mice harboring mutations of copper-zinc superoxide dismutase 1 (SOD1) in familial amyotrophic lateral sclerosis (ALS). Conversely, the loss of VEGF expression through genetic depletion can give rise to a phenotype resembling ALS independent of SOD1 mutations. Here, we observe a profound downregulation of VEGF mRNA expression in spinal cords of G93A SOD1 mice that occurred early in the course of the disease. Using an in vitro culture model of glial cells expressing mutant SOD1, we demonstrate destabilization and downregulation of VEGF RNA with concomitant loss of protein expression that correlates with level of transgene expression. Using a luciferase reporter assay, we show that this molecular effect is mediated through a portion of the VEGF 3'-untranslated region (UTR) that harbors a class II adenylate/uridylate-rich element. Other mutant forms of SOD1 produced a similar negative effect on luciferase RNA and protein expression. Mobility shift assay with a VEGF 3'-UTR probe reveals an aberrantly migrating complex that contains mutant SOD1. We further show that the RNA stabilizing protein, HuR (human antigen R), is translocated from nucleus to cytoplasm in mutant SOD1 cells in vitro and mouse motor neurons in vivo. In summary, our data suggest that mutant SOD1 gains a novel function, possibly by altering the ribonucleoprotein complex with the VEGF 3'-UTR. We postulate that the resultant dysregulation of VEGF posttranscriptional processing critically reduces the level of this neuroprotective growth factor and accelerates the neurodegenerative process in ALS.

Does treating schizophrenia reduce the chances of developing amyotrophic lateral sclerosis?

The development of amyotrophic lateral sclerosis (ALS) in the relatively common psychiatric disorder schizophrenia is very rare. This observation has been made by us and a number of other neuromuscular specialists at large ALS centers. We propose that the use of neuroleptics and some antidepressants, which are chronically prescribed to schizophrenics and which have neuroprotective properties and some of which promote neurogenesis, may confer protection against this deadly neurodegenerative disease ALS. Such an observation may have important implications towards the therapy and understanding the pathophysiology of this deadly neurodegenerative disease.

Dysequilibrium between caspases and their inhibitors in a mouse model for amyotrophic lateral sclerosis

Mutations in copper/zinc superoxide dismutase (SOD1) have been implicated in the pathogenesis of familial amyotrophic lateral sclerosis (ALS). Mutant SOD1 protein likely gains a novel cytotoxic property, leading to the death of motor neurons. We therefore investigated whether caspase-mediated apoptosis is associated with novel cytotoxic properties in a rodent model for familial ALS (G93A SOD1 transgenic mice). Caspase-9 (an effecter in the mitochondrial apoptotic pathway), caspase-8 (an effecter in the Fas apoptotic pathway), and caspase-3 (an executioner of both pathways) proteins were all present in nonactive forms in the spinal cords of wild-type mice during the early stage of the disease (8 weeks), at which time the mice had not yet exhibited motor paralysis. In transgenic mice, however, these proteins were present in their active forms, and their mRNA levels were significantly upregulated in the represent to this conversion from nonactive to active forms. During the advanced stage of the disease (16 weeks), when paralysis was evident, the active caspase levels were further elevated. On the other hand, the mRNA and protein levels of survivin, a counteraction protein against caspases, were significantly suppressed during the early stage, and sharply increased during the advanced stage. Although the mRNA and protein levels of X-linked inhibitor of apoptosis protein (XIAP) remained at the same levels as those seen in the control (wild-type mice) during the early stage, they were significantly depressed at an age of 16 weeks. These findings were observed exclusively in the spinal cord, the region responsible for the disease, and not in the cerebellum, a non-responsible region. We conclude that conditions facilitating the apoptotic process during the early stage of the disease play causative roles in the pathogenesis of ALS and that the suppression of XIAP levels during the advanced stage could contribute to disease expression and/or progression.

Formation of multinucleated giant cells and microglial degeneration in rats expressing a mutant Cu/Zn superoxide dismutase gene

BACKGROUND

Microglial neuroinflammation is thought to play a role in the pathogenesis of amyotrophic lateral sclerosis (ALS). The purpose of this study was to provide a histopathological evaluation of the microglial neuroinflammatory response in a rodent model of ALS, the SOD1G93A transgenic rat.

METHODS

Multiple levels of the CNS from spinal cord to cerebral cortex were studied in SOD1G93A transgenic rats during three stages of natural disease progression, including presymptomatic, early symptomatic (onset), and late symptomatic (end stage), using immuno- and lectin histochemical markers for microglia, such as OX-42, OX-6, and Griffonia simplicifolia isolectin B4.

RESULTS

Our studies revealed abnormal aggregates of microglia forming in the spinal cord as early as the presymptomatic stage. During the symptomatic stages there was prominent formation of multinucleated giant cells through fusion of microglial cells in the spinal cord, brainstem, and red nucleus of the midbrain. Other brain regions, including substantia nigra, cranial nerve nuclei, hippocampus and cortex showed normal appearing microglia. In animals during end stage disease at 4-5 months of age virtually all microglia in the spinal cord gray matter showed extensive fragmentation of their cytoplasm (cytorrhexis), indicative of widespread microglial degeneration. Few microglia exhibiting nuclear fragmentation (karyorrhexis) indicative of apoptosis were identified at any stage.

CONCLUSION

The current findings demonstrate the occurrence of severe abnormalities in microglia, such as cell fusions and cytorrhexis, which may be the result of expression of mutant SOD1 in these cells. The microglial changes observed are different from those that accompany normal microglial activation, and they demonstrate that aberrant activation and degeneration of microglia is part of the pathogenesis of motor neuron disease.

Correction of humoral derangements from mutant superoxide dismutase 1 spinal cord

OBJECTIVE

We sought to define molecular and cellular participants that mediate motor neuron injury in amyotrophic lateral sclerosis using a coculture system.

METHODS

We cocultured embryonic stem cell-derived motor neurons with organotypic slice cultures from wild-type or SOD1G93A (MT) mice. We examined axon lengths and cell survival of embryonic stem cell-derived motor neurons. We defined and quantified the humoral factors that differed between wild-type and MT organotypic cultures, and then corrected these differences in cell culture.

RESULTS

MT spinal cord organotypic slices were selectively toxic to motor neurons as defined by axonal lengths and cell survival. MT spinal cord organotypic slices secreted higher levels of nitric oxide, interleukin (IL)-1beta, IL-6, and IL-12p70 and lower levels of vascular endothelial growth factor. The toxicity of MT spinal cord organotypic cultures was reduced and axonal lengths were restored to near normal by coculturing in the presence of reactive oxygen species scavenger, vascular endothelial growth factor, and neutralizing antibodies to IL-1beta, IL-6, and IL-12.

INTERPRETATION

MT spinal cord organotypic cultures overexpress certain factors and underexpress others, creating a nonpermissive environment for cocultured motor neurons. Correction of these abnormalities as a group, but not individually, restores axonal length to near normal. Such a "cocktail" approach to the treatment of amyotrophic lateral sclerosis should be investigated further.

Glia cells in amyotrophic lateral sclerosis: New clues to understanding an old disease?

In classic neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), the pathogenic concept of a cell-autonomous disease of motor neurons has been challenged increasingly in recent years. Macro- and microglial cells have come to the forefront for their role in multistep degenerative processes in ALS and respective disease models. The activation of astroglial and microglial cells occurs early in the pathogenesis of the disease and seems to greatly influence disease onset and promotion. The role of oligodendrocytes and Schwann cells remains elusive. In this review we highlight the impact of nonneuronal cells in ALS pathology. We discuss diverse glial membrane proteins that are necessary to control neuronal activity and neuronal cell survival, and summarize the contribution of these proteins to motor neuron death in ALS. We also describe recently discovered glial mechanisms that promote motor neuron degeneration using state-of-the-art genetic mouse technology. Finally, we provide an outlook on the extent to which these new pathomechanistic insights may offer novel therapeutic approaches.

Absence of tumor necrosis factor-alpha does not affect motor neuron disease caused by superoxide dismutase 1 mutations

An increase in the expression of the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) has been observed in patients with amyotrophic lateral sclerosis (ALS) and in the mice models of the disease. TNF-alpha is a potent activator of macrophages and microglia and, under certain conditions, can induce or exacerbate neuronal cell death. Here, we assessed the contribution of TNF-alpha in motor neuron disease in mice overexpressing mutant superoxide dismutase 1 (SOD1) genes linked to familial ALS. This was accomplished by the generation of mice expressing SOD1(G37R) or SOD1(G93A) mutants in the context of TNF-alpha gene knock out. Surprisingly, the absence of TNF-alpha did not affect the lifespan or the extent of motor neuron loss in SOD1 transgenic mice. These results provide compelling evidence indicating that TNF-alpha does not directly contribute to motor neuron degeneration caused by SOD1 mutations.

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.

On the relation of oxidative stress to neuroinflammation: lessons learned from the G93A-SOD1 mouse model of amyotrophic lateral sclerosis

The central nervous system (CNS) presents both challenges and opportunities to researchers of redox biochemistry. The CNS is sensitive to oxidative damage during aging or disease; excellent transgenic models of specific neurodegenerative diseases have been created that reproduce oxidative stress components of the corresponding human disorder. Mouse models of familial amyotrophic lateral sclerosis (ALS) based on overexpressed mutant human Cu, Zn-superoxide dismutase (SOD1) are cases in point. These animals experience predictably staged, age-dependent motor neuron degeneration with profound cellular and biochemical damage to nerve fibers and spinal cord tissue. Severe protein and lipid oxidation occurs in these animals, apparently as an indirect consequence of protein aggregation or cytopathic protein-protein interactions, as opposed to aberrant redox catalysis by the mutant enzyme. Recent studies of G93A-SOD1 mice and rats suggest that oxidative damage is part of an unmitigated neuroinflammatory reaction, possibly arising in combination from mitochondrial dysfunction plus pathophysiologic activation of both astrocytes and microglia. Lesions to redox signal-transduction pathways in mutant SOD1+ glial cells may stimulate broad-spectrum upregulation of proinflammatory genes, including arachidonic acid-metabolizing enzymes [e.g., cyclooxygenase-II (COX-II) and 5-lipoxygenase (5LOX)]; nitric oxide synthase (NOS) isoforms; cytokines (particularly tumor necrosis factor alpha, TNF-alpha); chemokines; and immunoglobulin Fc receptors (FcgammaRs). The integration of these processes creates a paracrine milieu inconsistent with healthy neural function. This review summarizes what has been learned to date from studies of mutant SOD1 transgenic animals and demonstrates that the G93A-SOD1 mouse in particular is a robust laboratory for the study of neuroinflammation and redox biochemistry.

Oxidative stress in ALS: A mechanism of neurodegeneration and a therapeutic target

The cause(s) of amyotrophic lateral sclerosis (ALS) is not fully understood in the vast majority of cases and the mechanisms involved in motor neuron degeneration are multi-factorial and complex. There is substantial evidence to support the hypothesis that oxidative stress is one mechanism by which motor neuron death occurs. This theory becomes more persuasive with the discovery that mutation of the anti-oxidant enzyme, superoxide dismutase 1 (SOD1), causes disease in a significant minority of cases. However, the precise mechanism(s) by which mutant SOD1 leads to motor neuron degeneration have not been defined with certainty, and trials of anti-oxidant therapies have been disappointing. Here, we review the evidence implicating oxidative stress in ALS pathogenesis, discuss how oxidative stress may affect and be affected by other proposed mechanisms of neurodegeneration, and review the trials of various anti-oxidants as potential therapies for ALS.

Innate immunity in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition in which motor neurons are selectively targeted. Although the underlying cause remains unclear, evidence suggests a role for innate immunity in disease pathogenesis. Neuroinflammation in areas of motor neuron loss is evident in presymptomatic mouse models of ALS and in human patients. Efforts aimed at attenuating the inflammatory response in ALS animal models have delayed symptom onset and extended survival. Seemingly conversely, attempts to sensitize cells of the innate immune system and modulate their phenotype have also shown efficacy. Effectors of innate immunity in the CNS appear to have ambivalent potential to promote either repair or injury. Because ALS is a syndromic disease in which glutamate excitotoxicity, altered cytoskeletal protein metabolism, oxidative injury, mitochondrial dysfunction and neuroinflammation all contribute to motor neuron degeneration, targeting inflammation via modulation of microglial function therefore holds significant potential as one aspect of therapeutic intervention and could provide insight into the exclusive vulnerability of motor neurons.

Molecular biology of amyotrophic lateral sclerosis: insights from genetics

Amyotrophic lateral sclerosis (ALS) is a paralytic disorder caused by motor neuron degeneration. Mutations in more than 50 human genes cause diverse types of motor neuron pathology. Moreover, defects in five Mendelian genes lead to motor neuron disease, with two mutations reproducing the ALS phenotype. Analyses of these genetic effects have generated new insights into the diverse molecular pathways involved in ALS pathogenesis. Here, we present an overview of the mechanisms for motor neuron death and of the role of non-neuronal cells in ALS.