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

Newly Synthesized Indolylacetic Derivatives Reduce Tumor Necrosis Factor-Mediated Neuroinflammation and Prolong Survival in Amyotrophic Lateral Sclerosis Mice

The debilitating neurodegenerative disease known as amyotrophic lateral sclerosis (ALS) is characterized by the progressive loss of motor neurons (MNs) in the brain, spinal cord, and motor cortex. The ALS neuroinflammatory component is being characterized and includes the overexpression of mediators, such as inducible nitric oxide synthase (iNOS) and tumor necrosis factor-α (TNF-α). Currently, there are no effective treatments for ALS. Indeed, riluzole, an N-methyl-D-aspartate (NMDA) glutamate receptor blocker, and edaravone, a reactive oxygen species (ROS) scavenger, are currently the sole two medications approved for ALS treatment. However, their efficacy in extending life expectancy typically amounts to only a few months. In order to improve the medicaments for the treatment of neurodegenerative diseases, preferably ALS, novel substituted 2-methyl-3-indolylacetic derivatives (compounds II-IV) were developed by combining the essential parts of two small molecules, namely, the opioids containing a 4-piperidinyl ring with indomethacin, previously shown to be efficacious in different experimental models of neuroinflammation. The synthesized compounds were evaluated for their potential capability of slowing down neurodegeneration associated with ALS progression in preclinical models of the disease in vitro and in vivo. Notably, we produced data to demonstrate that the treatment with the newly synthesized compound III: (1) prevented the upregulation of TNF-α observed in BV-2 microglial cells exposed to the toxin lipopolysaccharides (LPS), (2) preserved SHSY-5Y cell survival exposed to β-N-methylamino-l-alanine (L-BMAA) neurotoxin, and (3) mitigated motor symptoms and improved survival rate of SOD1G93A ALS mice. In conclusion, the findings of the present work support the potential of the synthesized indolylacetic derivatives II-IV in ALS treatment. Indeed, in the attempt to realize an association between two active molecules, we assumed that the combination of the indispensable moieties of two small molecules (the opioids containing a 4-piperidinyl ring with the FANS indomethacin) might lead to new medicaments potentially useful for the treatment of amyotrophic lateral sclerosis.

Umbilical cord mesenchymal stem cell-conditioned medium inhibits microglial activation to ameliorate neuroinflammation in amyotrophic lateral sclerosis mice and cell models

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease for which few effective therapeutic strategies are available. Increasing evidence indicates that neuroinflammation plays a significant role in ALS pathogenesis. Mesenchymal stem cell (MSC)-based therapy has been proposed for the treatment of neurodegenerative diseases, including ALS. In this study, we first demonstrated that systemic administration of conditioned medium derived from umbilical cord MSCs (UCMSC-CM) extends the lifespan of transgenic SOD1-G93A mice, a well-characterized model of familial ALS. Moreover, UCMSC-CM inhibits microglial activation and astrogliosis and alleviates the inflammatory milieu by reducing the release of proinflammatory cytokines and the expression of iNOS in the spinal cord. Using BV-2 cells overexpressing the SOD1-G93A mutant as an ALS cellular model, we uncovered that UCMSC-CM also suppresses the lipopolysaccharide (LPS)-induced inflammatory response, including reduced expression of proinflammatory cytokines and iNOS. Importantly, by culturing astrocytes alone in microglia-conditioned medium (MCM) or together with microglia in a transwell coculture system, we found that UCMSC-CM modulates the secretome of microglia exposed to inflammatory stimuli, thereby preventing the conversion of astrocytes to the A1 neurotoxic phenotype. This study revealed the anti-inflammatory properties of UCMSC-CM and its regulatory effect on glial activation in the treatment of neuroinflammation in ALS, providing strong evidence for the clinical application of UCMSC-CM.

The contribution of the peripheral immune system to neurodegeneration

Microglial cells are the major immune cells of the central nervous system (CNS), and directly react to neurodegeneration, but other immune cell types are also able to react to pathology and can modify the course of neurodegenerative processes. These mainly include monocytes/macrophages and lymphocytes. While these peripheral immune cells were initially considered to act only after infiltrating the CNS, recent evidence suggests that some of them can also act directly from the periphery. We will review the existing and emerging evidence for a role of peripheral immune cells in neurodegenerative diseases, both with and without CNS infiltration. Our focus will be on amyotrophic lateral sclerosis, but we will also compare to Alzheimer's disease and Parkinson's disease to highlight similarities or differences. Peripheral immune cells are easily accessible, and therefore may be an attractive therapeutic target for neurodegenerative diseases. Thus, understanding how these peripheral immune cells communicate with the CNS deserves deeper investigation.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Anti-apoptotic Splicing Variant of AIMP2 Recover Mutant SOD1-Induced Neuronal Cell Death

Although a couple of studies have reported that mutant superoxide dismutase 1 (SOD1), one of the causative genes of familial amyotrophic lateral, interacts physically with lysyl-tRNA synthetase (KARS1) by a gain of function, there is limited evidence regarding the detailed mechanism about how the interaction leads to neuronal cell death. Our results indicated that the aminoacyl-tRNA synthetase-interacting multi-functional protein 2 (AIMP2) mediated cell death upon the interplay between mutant SOD1 and KARS1 in ALS. Binding of mutant SOD1 with KARS1 led to the release of AIMP2 from its original binding partner KARS1, and the free form of AIMP2 induced TRAF2 degradation followed by TNF-α-induced cell death. We also suggest a therapeutic application that overexpression of DX2, the exon 2-deleted antagonistic splicing variant of AIMP2 (AIMP2-DX2), reduced neuronal cell death in the ALS mouse model. Expression of DX2 suppressed TRAF2 degradation and TNF-α-induced cell death by competing mode of action against full-length AIMP2. Motor neuron differentiated form iPSC showed a resistance in neuronal cell death after DX2 administration. Further, intrathecal administration of DX2-coding adeno-associated virus (AAV) improved locomotive activity and survival in a mutant SOD1-induced ALS mouse model. Taken together, these results indicated that DX2 could prolong life span and delay the ALS symptoms through compensation in neuronal inflammation.

Targeting TNFα produced by astrocytes expressing amyotrophic lateral sclerosis-linked mutant fused in sarcoma prevents neurodegeneration and motor dysfunction in mice

Genetic mutations that cause amyotrophic lateral sclerosis (ALS), a progressively lethal motor neuron disease, are commonly found in ubiquitously expressed genes. In addition to direct defects within motor neurons, growing evidence suggests that dysfunction of non-neuronal cells is also an important driver of disease. Previously, we demonstrated that mutations in DNA/RNA binding protein fused in sarcoma (FUS) induce neurotoxic phenotypes in astrocytes in vitro, via activation of the NF-κB pathway and release of pro-inflammatory cytokine TNFα. Here, we developed an intraspinal cord injection model to test whether astrocyte-specific expression of ALS-causative FUSR521G variant (mtFUS) causes neuronal damage in vivo. We show that restricted expression of mtFUS in astrocytes is sufficient to induce death of spinal motor neurons leading to motor deficits through upregulation of TNFα. We further demonstrate that TNFα is a key toxic molecule as expression of mtFUS in TNFα knockout animals does not induce pathogenic changes. Accordingly, in mtFUS-transduced animals, administration of TNFα neutralizing antibodies prevents neurodegeneration and motor dysfunction. Together, these studies strengthen evidence that astrocytes contribute to disease in ALS and establish, for the first time, that FUS-ALS astrocytes induce pathogenic changes to motor neurons in vivo. Our work identifies TNFα as the critical driver of mtFUS-astrocytic toxicity and demonstrates therapeutic success of targeting TNFα to attenuate motor neuron dysfunction and death. Ultimately, through defining and subsequently targeting this toxic mechanism, we provide a viable FUS-ALS specific therapeutic strategy, which may also be applicable to sporadic ALS where FUS activity and cellular localization are frequently perturbed.

A chemogenomic approach is required for effective treatment of amyotrophic lateral sclerosis

ALS is a fatal untreatable disease involving degeneration of motor neurons. Μultiple causative genes encoding proteins with versatile functions have been identified indicating that diverse biological pathways lead to ALS. Chemical entities still represent a promising choice to delay ALS progression, attenuate symptoms and/or increase life expectancy, but also gene-based and stem cell-based therapies are in the process of development, and some are tested in clinical trials. Various compounds proved effective in transgenic models overexpressing distinct ALS causative genes unfortunately though, they showed no efficacy in clinical trials. Notably, while animal models provide a uniform genetic background for preclinical testing, ALS patients are not stratified, and the distinct genetic forms of ALS are treated as one group, which could explain the observed discrepancies between treating genetically homogeneous mice and quite heterogeneous patient cohorts. We suggest that chemical entity-genotype correlation should be exploited to guide patient stratification for pharmacotherapy, that is administered drugs should be selected based on the ALS genetic background.

Non-neuronal cells in amyotrophic lateral sclerosis - from pathogenesis to biomarkers

The prevailing motor neuron-centric view of amyotrophic lateral sclerosis (ALS) pathogenesis could be an important factor in the failure to identify disease-modifying therapy for this neurodegenerative disorder. Non-neuronal cells have crucial homeostatic functions within the CNS and evidence of involvement of these cells in the pathophysiology of several neurodegenerative disorders, including ALS, is accumulating. Microglia and astrocytes, in crosstalk with peripheral immune cells, can exert both neuroprotective and adverse effects, resulting in a highly nuanced range of neuronal and non-neuronal cell interactions. This Review provides an overview of the diverse roles of non-neuronal cells in relation to the pathogenesis of ALS and the emerging potential of non-neuronal cell biomarkers to advance therapeutic development.

Oxaloacetate treatment preserves motor function in SOD1G93A mice and normalizes select neuroinflammation-related parameters in the spinal cord

Amyotrophic lateral sclerosis (ALS) remains a devastating motor neuron disease with limited treatment options. Oxaloacetate treatment has a neuroprotective effect in rodent models of seizure and neurodegeneration. Therefore, we treated the ALS model superoxide dismutase 1 (SOD1) G93A mice with oxaloacetate and evaluated their neuromuscular function and lifespan. Treatment with oxaloacetate beginning in the presymptomatic stage significantly improved neuromuscular strength measured during the symptomatic stage in the injected mice compared to the non-treated group. Oxaloacetate treatment starting in the symptomatic stage significantly delayed limb paralysis compared with the non-treated group. For lifespan analysis, oxaloacetate treatment did not show a statistically significant positive effect, but the treatment did not shorten the lifespan. Mechanistically, SOD1G93A mice showed increased levels of tumor necrosis factor-α (TNFα) and peroxisome proliferative activated receptor gamma coactivator 1α (PGC-1α) mRNAs in the spinal cord. However, oxaloacetate treatment reverted these abnormal levels to that of wild-type mice. Similarly, the altered expression level of total NF-κB protein returned to that of wild-type mice with oxaloacetate treatment. These results suggest that the beneficial effects of oxaloacetate treatment in SOD1G93A mice may reflect the effects on neuroinflammation or bioenergetic stress.

Tumor Necrosis Factor Alpha in Amyotrophic Lateral Sclerosis: Friend or Foe?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by a massive neuroinflammatory reaction, which plays a key role in the progression of the disease. One of the major mediators of the inflammatory response is the pleiotropic cytokine tumor necrosis factor α (TNFα), mainly released within the central nervous system (CNS) by reactive astrocytes and microglia. Increased levels of TNFα and its receptors (TNFR1 and TNFR2) have been described in plasma, serum, cerebrospinal fluid and CNS tissue from both ALS patients and transgenic animal models of disease. However, the precise role exerted by TNFα in the context of ALS is still highly controversial, since both protective and detrimental functions have been reported. These opposing actions depend on multiple factors, among which includes the type of TNFα receptor activated. In fact, TNFR2 seems to mediate a harmful role being involved in motor neuron cell death, whereas TNFR1 signaling mediates neuroprotective effects, promoting the expression and secretion of trophic factors. This suggests that a better understanding of the cytokine impact on ALS progression may enable the development of effective therapies aimed at strengthening the protective roles of TNFα and at suppressing the detrimental ones.

The microglial component of amyotrophic lateral sclerosis

Microglia are the primary immune cells of the CNS, carrying out key homeostatic roles and undergoing context-dependent and temporally regulated changes in response to injury and neurodegenerative diseases. Microglia have been implicated in playing a role in amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by extensive motor neuron loss leading to paralysis and premature death. However, as the pathomechansims of ALS are increasingly recognized to involve a multitude of different cell types, it has been difficult to delineate the specific contribution of microglia to disease. Here, we review the literature of microglial involvement in ALS and discuss the evidence for the neurotoxic and neuroprotective pathways that have been attributed to microglia in this disease. We also discuss accumulating evidence for spatiotemporal regulation of microglial activation in this context. A deeper understanding of the role of microglia in the ‘cellular phase’ of ALS is crucial in the development of mechanistically rationalized therapies.

Knockout of reactive astrocyte activating factors slows disease progression in an ALS mouse model

Reactive astrocytes have been implicated in the pathogenesis of neurodegenerative diseases, including a non-cell autonomous effect on motor neuron survival in ALS. We previously defined a mechanism by which microglia release three factors, IL-1α, TNFα, and C1q, to induce neurotoxic astrocytes. Here we report that knocking out these three factors markedly extends survival in the SOD1^G93A ALS mouse model, providing evidence for gliosis as a potential ALS therapeutic target.

Peripheral proinflammatory Th1/Th17 immune cell shift is linked to disease severity in amyotrophic lateral sclerosis

Neuroinflammation is involved in the pathogenesis of amyotrophic lateral sclerosis (ALS), but only limited data are available on systematic peripheral and central immune cell profiles in ALS. We studied detailed immune profiles of 73 ALS patients and 48 healthy controls (controls) in peripheral blood by fluorescence-activated cell sorting as well as cytokine expression profiles in serum. In a subgroup of 16 ALS patients and 10 controls we additionally studied cerebrospinal fluid (CSF) samples. In peripheral blood, T cell subtypes presented a shift towards pro-inflammatory Th 1 and Th 17 cells whereas anti-inflammatory Th2 and T regulatory cells were decreased. Important players in innate immunity including distinct monocyte (Mo) and natural killer (NK) cell subtypes were changed in ALS patients compared to controls. Pro-inflammatory serum cytokines such as interleukin (IL)-1 beta, IL-6 and interferon-gamma (IFN-gamma) were increased and the anti-inflammatory cytokine IL-10 was decreased. Correlation analysis revealed moderate negative correlations between Th1 and Th17 to the ALS functional rating scale revised (ALSFRS-R) and to forced vital capacity. In CSF samples, no relevant alteration of the immune profile was found. In conclusion, the immune profile in ALS was shifted towards a Th1/Th17 cell-mediated pro-inflammatory immune response and correlated to disease severity and progression. Large prospective studies are needed to confirm these findings.

Glia in amyotrophic lateral sclerosis and spinal cord injury: common therapeutic targets

The toolkit for repairing damaged neurons in amyotrophic lateral sclerosis (ALS) and spinal cord injury (SCI) is extremely limited. Here, we reviewed the in vitro and in vivo studies and clinical trials on nonneuronal cells in the neurodegenerative processes common to both these conditions. Special focus was directed to microglia and astrocytes, because their activation and proliferation, also known as neuroinflammation, is a key driver of neurodegeneration. Neuroinflammation is a multifaceted process that evolves during the disease course, and can be either beneficial or toxic to neurons. Given the fundamental regulatory functions of glia, pathogenic mechanisms in neuroinflammation represent promising therapeutic targets. We also discussed neuroprotective, immunosuppressive, and stem-cell based approaches applicable to both ALS and SCI.

Glia in amyotrophic lateral sclerosis and spinal cord injury: common therapeutic targets

The toolkit for repairing damaged neurons in amyotrophic lateral sclerosis (ALS) and spinal cord injury (SCI) is extremely limited. Here, we reviewed the in vitro and in vivo studies and clinical trials on nonneuronal cells in the neurodegenerative processes common to both these conditions. Special focus was directed to microglia and astrocytes, because their activation and proliferation, also known as neuroinflammation, is a key driver of neurodegeneration. Neuroinflammation is a multifaceted process that evolves during the disease course, and can be either beneficial or toxic to neurons. Given the fundamental regulatory functions of glia, pathogenic mechanisms in neuroinflammation represent promising therapeutic targets. We also discussed neuroprotective, immunosuppressive, and stem-cell based approaches applicable to both ALS and SCI.

A Combination of Intrathecal and Intramuscular Application of Human Mesenchymal Stem Cells Partly Reduces the Activation of Necroptosis in the Spinal Cord of SOD1G93A Rats

An increasing number of studies have demonstrated the beneficial effects of human mesenchymal stem cells (hMSC) in the treatment of amyotrophic lateral sclerosis (ALS). We compared the effect of repeated intrathecal applications of hMSC or their conditioned medium (CondM) using lumbar puncture or injection into the muscle (quadriceps femoris), or a combination of both applications in symptomatic SOD1^G93A rats. We further assessed the effect of the treatment on three major cell death pathways (necroptosis, apoptosis, and autophagy) in the spinal cord tissue. All the animals were behaviorally tested (grip strength test, Basso Beattie Bresnahan (BBB) test, and rotarod), and the tissue was analyzed immunohistochemically, by qPCR and Western blot. All symptomatic SOD1 rats treated with hMSC had a significantly increased lifespan, improved motor activity and reduced number of Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive cells. Moreover, a combined hMSC delivery increased motor neuron survival, maintained neuromuscular junctions in quadriceps femoris and substantially reduced the levels of proteins involved in necroptosis (Rip1, mixed lineage kinase‐like protein, cl‐casp8), apoptosis (cl‐casp 9) and autophagy (beclin 1). Furthermore, astrogliosis and elevated levels of Connexin 43 were decreased after combined hMSC treatment. The repeated application of CondM, or intramuscular injections alone, improved motor activity; however, this improvement was not supported by changes at the molecular level. Our results provide new evidence that a combination of repeated intrathecal and intramuscular hMSC applications protects motor neurons and neuromuscular junctions, not only through a reduction of apoptosis and autophagy but also through the necroptosis pathway, which is significantly involved in cell death in rodent SOD1^G93A model of ALS. stem cells translational medicine2019;8:535–547

The Genetic Diagnosis of Neurodegenerative Diseases and Therapeutic Perspectives

Genetics has led to a new focus regarding approaches to the most prevalent diseases today. Ascertaining the molecular secrets of neurodegenerative diseases will lead to developing drugs that will change natural history, thereby affecting the quality of life and mortality of patients. The sequencing of candidate genes in patients suffering neurodegenerative pathologies is faster, more accurate, and has a lower cost, thereby enabling algorithms to be proposed regarding the risk of neurodegeneration onset in healthy persons including the year of onset and neurodegeneration severity. Next generation sequencing has resulted in an explosion of articles regarding the diagnosis of neurodegenerative diseases involving exome sequencing or sequencing a whole gene for correlating phenotypical expression with genetic mutations in proteins having key functions. Many of them occur in neuronal glia, which can trigger a proinflammatory effect leading to defective proteins causing sporadic or familial mutations. This article reviews the genetic diagnosis techniques and the importance of bioinformatics in interpreting results from neurodegenerative diseases. Risk scores must be established in the near future regarding diseases with a high incidence in healthy people for defining prevention strategies or an early start for giving drugs in the absence of symptoms.

Astrocyte elevated gene-1 is a novel regulator of astrogliosis and excitatory amino acid transporter-2 via interplaying with nuclear factor-κB signaling in astrocytes from amyotrophic lateral sclerosis mouse model with hSOD1G93A mutation

AEG-1 has received extensive attention on cancer research. However, little is known about its roles in astrogliosis of Amyotrophic lateral sclerosis (ALS). In this study, we detected AEG-1 expression in hSOD1G93A-positive (mut-SOD1) astrocytes and wild type (wt-SOD1) astrocytes, and intend to elucidate its potential functions in ALS related astrogliosis and the always accompanied dysregulated glutamate clearance. Results showed elevated protein and mRNA levels of AEG-1 in mut-SOD1 astrocytes; Also, NF-κB signaling pathway related proteins and inflammatory cytokines were upregulated in mut-SOD1 astrocytes; AEG-1 knockdown attenuated astrocytes proliferation and pro-inflammatory release; also we found that AEG-1 silence inhibited translocation of p65 from cytoplasma to nuclear, which was associated with inhibited NF-κB signaling. Besides, excitatory amino acid transporter-2 (EAAT2) expression levels were significantly decreased, accompanied by impaired glutamate clearance ability, in mut-SOD1 astrocytes; yin yang 1 (YY1), a transcriptional inhibitor for EAAT2, increased in nucleus of mut-SOD1 astrocytes. AEG-1 silence inhibited translocation of YY1 to nucleus, increased EAAT2 expression levels, and enhanced astrocytic ability of glutamate clearance, ultimately exerted the neuronal protection. Findings from this study implicate potential function of AEG-1 in mut-SOD1 related astrogliosis and the accompanied excitatory cytotoxic mechanism in ALS.

Intrathecal Injection of scAAV9-hIGF1 Prolongs the Survival of ALS Model Mice by Inhibiting the NF-kB Pathway

Amyotrophic lateral sclerosis (ALS) is a chronic, fatal neurodegenerative disorder characterized by the progressive loss of upper and lower motor neurons. Currently, there is no effective drug for ALS. Recent studies in ALS model mice have shown that insulin-like growth factor-1 (IGF1) may be a promising therapeutic drug. We demonstrate that self-complementary adeno-associated virus serum type 9 encoding the human IGF1 (scAAV9-hIGF1) could significantly postpone the onset and slow down the progression of the disease owning to inhibiting the NF-κB signaling pathway. Furthermore, the results were supported by experiments in which the CRISPR/Cas9 system was used to knock-down IGF1 in ALS mice (mIGF1). Our data indicate that IGF1-mediated suppression of NF-κB activation in microglia is a novel molecular mechanism underlying MN death in ALS. It provides new insight into IGF1 and points toward novel therapeutic targets of IGF1 in ALS.

Astrocytes expressing ALS-linked mutant FUS induce motor neuron death through release of tumor necrosis factor-alpha

Mutations in fused in sarcoma (FUS) are linked to amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease affecting both upper and lower motor neurons. While it is established that astrocytes contribute to the death of motor neurons in ALS, the specific contribution of mutant FUS (mutFUS) through astrocytes has not yet been studied. Here, we used primary astrocytes expressing a N‐terminally GFP tagged R521G mutant or wild‐type FUS (WTFUS) and show that mutFUS‐expressing astrocytes undergo astrogliosis, damage co‐cultured motor neurons via activation of an inflammatory response and produce conditioned medium (ACM) that is toxic to motor neurons in isolation. Time lapse imaging shows that motor neuron cultures exposed to mutFUS ACM, but not WTFUS ACM, undergo significant cell loss, which is preceded by progressive degeneration of neurites. We found that Tumor Necrosis Factor‐Alpha (TNFα) is secreted into ACM of mutFUS‐expressing astrocytes. Accordingly, mutFUS astrocyte‐mediated motor neuron toxicity is blocked by targeting soluble TNFα with neutralizing antibodies. We also found that mutant astrocytes trigger changes to motor neuron AMPA receptors (AMPAR) that render them susceptible to excitotoxicity and AMPAR‐mediated cell death. Our data provide the first evidence of astrocytic involvement in FUS‐ALS, identify TNFα as a mediator of this toxicity, and provide several potential therapeutic targets to protect motor neurons in FUS‐linked ALS.

Amyotrophic Lateral Sclerosis, a Multisystem Pathology: Insights into the Role of TNFα

Amyotrophic lateral sclerosis (ALS) is considered a multifactorial, multisystem disease in which inflammation and the immune system play important roles in development and progression. The pleiotropic cytokine TNFα is one of the major players governing the inflammation in the central nervous system and peripheral districts such as the neuromuscular and immune system. Changes in TNFα levels are reported in blood, cerebrospinal fluid, and nerve tissues of ALS patients and animal models. However, whether they play a detrimental or protective role on the disease progression is still not clear. Our group and others have recently reported opposite involvements of TNFR1 and TNFR2 in motor neuron death. TNFR2 mediates TNFα toxic effects on these neurons presumably through the activation of MAP kinase-related pathways. On the other hand, TNFR2 regulates the function and proliferation of regulatory T cells (Treg) whose expression is inversely correlated with the disease progression rate in ALS patients. In addition, TNFα is considered a procachectic factor with a direct catabolic effect on skeletal muscles, causing wasting. We review and discuss the role of TNFα in ALS in the light of its multisystem nature.

The Dual Role of Microglia in ALS: Mechanisms and Therapeutic Approaches

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by a non-cell autonomous motor neuron loss. While it is generally believed that the disease onset takes place inside motor neurons, different cell types mediating neuroinflammatory processes are considered deeply involved in the progression of the disease. On these grounds, many treatments have been tested on ALS animals with the aim of inhibiting or reducing the pro-inflammatory action of microglia and astrocytes and counteract the progression of the disease. Unfortunately, these anti-inflammatory therapies have been only modestly successful. The non-univocal role played by microglia during stress and injuries might explain this failure. Indeed, it is now well recognized that, during ALS, microglia displays different phenotypes, from surveillant in early stages, to activated states, M1 and M2, characterized by the expression of respectively harmful and protective genes in later phases of the disease. Consistently, the inhibition of microglial function seems to be a valid strategy only if the different stages of microglia polarization are taken into account, interfering with the reactivity of microglia specifically targeting only the harmful pathways and/or potentiating the trophic ones. In this review article, we will analyze the features and timing of microglia activation in the light of M1/M2 phenotypes in the main mice models of ALS. Moreover, we will also revise the results obtained by different anti-inflammatory therapies aimed to unbalance the M1/M2 ratio, shifting it towards a protective outcome.

Optineurin in amyotrophic lateral sclerosis: Multifunctional adaptor protein at the crossroads of different neuroprotective mechanisms

When optineurin mutations showed up on the amyotrophic lateral sclerosis (ALS) landscape in 2010, they differed from most other ALS-causing genes. They seemed to act by loss- rather than gain-of-function, and it was unclear how a polyubiquitin-binding adaptor protein, which was proposed to regulate a variety of cellular functions including cell signaling and vesicle trafficking, could mediate neuroprotection. This review discusses the considerable progress that has been made since then. A large number of mutations in optineurin and optineurin-interacting proteins TANK-binding kinase (TBK1) and p62/SQSTM-1 have been found in the ALS patients, suggesting a common neuroprotective pathway. Moreover, functional studies of the ALS-causing optineurin mutations and the recently established optineurin ubiquitin-binding deficient and knockout mouse models helped identify three major mechanisms likely to mediate neuroprotection: regulation of autophagy, mitigation of (chronic) inflammatory signaling, and blockade of necroptosis. These three processes crosstalk, and require multiple levels of control, many of which can be mediated by optineurin. Based on the role of optineurin in multiple processes and the unexpected finding that targeted optineurin deletion in microglia and oligodendrocytes ultimately leads to the same phenotype of axonal degeneration despite different initial defects, we propose that the failure of the weakest link in the optineurin neuroprotective network is sufficient to disturb homeostasis and set-off the domino effect that could ultimately lead to neurodegeneration.

Role and Therapeutic Potential of Astrocytes in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of motor neurons in the spinal cord, brain stem, and motor cortex. The molecular mechanism underlying the progressive degeneration of motor neuron remains uncertain but involves a non-cell autonomous process. In acute injury or degenerative diseases astrocytes adopt a reactive phenotype known as astrogliosis. Astrogliosis is a complex remodeling of astrocyte biology and most likely represents a continuum of potential phenotypes that affect neuronal function and survival in an injury-specific manner. In ALS patients, reactive astrocytes surround both upper and lower degenerating motor neurons and play a key role in the pathology. It has become clear that astrocytes play a major role in ALS pathology. Through loss of normal function or acquired new characteristics, astrocytes are able to influence motor neuron fate and the progression of the disease. The use of different cell culture models indicates that ALS-astrocytes are able to induce motor neuron death by secreting a soluble factor(s). Here, we discuss several pathogenic mechanisms that have been proposed to explain astrocyte-mediated motor neuron death in ALS. In addition, examples of strategies that revert astrocyte-mediated motor neuron toxicity are reviewed to illustrate the therapeutic potential of astrocytes in ALS. Due to the central role played by astrocytes in ALS pathology, therapies aimed at modulating astrocyte biology may contribute to the development of integral therapeutic approaches to halt ALS progression.

Disruption of the astrocytic TNFR1-GDNF axis accelerates motor neuron degeneration and disease progression in amyotrophic lateral sclerosis

Considerable evidence indicates that neurodegeneration in amyotrophic lateral sclerosis (ALS) can be conditioned by a deleterious interplay between motor neurons and astrocytes. Astrocytes are the major glial component in the central nervous system (CNS) and fulfill several activities that are essential to preserve CNS homeostasis. In physiological and pathological conditions, astrocytes secrete a wide range of factors by which they exert multimodal influences on their cellular neighbours. Among others, astrocytes can secrete glial cell line-derived neurotrophic factor (GDNF), one of the most potent protective agents for motor neurons. This suggests that the modulation of the endogenous mechanisms that control the production of astrocytic GDNF may have therapeutic implications in motor neuron diseases, particularly ALS. In this study, we identified TNF receptor 1 (TNFR1) signalling as a major promoter of GDNF synthesis/release from human and mouse spinal cord astrocytes in vitro and in vivo To determine whether endogenously produced TNFα can also trigger the synthesis of GDNF in the nervous system, we then focused on SOD1^G93A ALS transgenic mice, whose affected tissues spontaneously exhibit high levels of TNFα and its receptor 1 at the onset and symptomatic stage of the disease. In SOD1^G93A spinal cords, we verified a strict correlation in the expression of the TNFα, TNFR1 and GDNF triad at different stages of disease progression. Yet, ablation of TNFR1 completely abolished GDNF rises in both SOD1^G93A astrocytes and spinal cords, a condition that accelerated motor neuron degeneration and disease progression. Our data suggest that the astrocytic TNFR1-GDNF axis represents a novel target for therapeutic intervention in ALS.

IL-10 Controls Early Microglial Phenotypes and Disease Onset in ALS Caused by Misfolded Superoxide Dismutase 1

While reactive microgliosis is a hallmark of advanced stages of amyotrophic lateral sclerosis (ALS), the role of microglial cells in events initiating and/or precipitating disease onset is largely unknown. Here we provide novel in vivo evidence of a distinct adaptive shift in functional microglial phenotypes in preclinical stages of superoxide dismutase 1 (SOD1)-mutant-mediated disease. Using a mouse model for live imaging of microglial activation crossed with SOD1(G93A) and SOD1(G37R) mouse models, we discovered that the preonset phase of SOD1-mediated disease is characterized by development of distinct anti-inflammatory profile and attenuated innate immune/TLR2 responses to lipopolysaccharide (LPS) challenge. This microglial phenotype was associated with a 16-fold overexpression of anti-inflammatory cytokine IL-10 in baseline conditions followed by a 4.5-fold increase following LPS challenge. While infusion of IL-10R blocking antibody, initiated at day 60, caused a significant increase in markers of microglial activation and precipitated clinical onset of disease, a targeted overexpression of IL-10 in microglial cells, delivered via viral vectors expressed under CD11b promoter, significantly delayed disease onset and increased survival of SOD1(G93A) mice. We propose that the high IL-10 levels in resident microglia in early ALS represent a homeostatic and compensatory "adaptive immune escape" mechanism acting as a nonneuronal determinant of clinical onset of disease. Significance statement: We report here for the first time that changing the immune profile of brain microglia may significantly affect clinical onset and duration of disease in ALS models. We discovered that in presymptomatic disease microglial cells overexpress anti-inflammatory cytokine IL-10. Given that IL-10 is major homeostatic cytokine and its production becomes deregulated with aging, this may suggest that the capacity of microglia to adequately produce IL-10 may be compromised in ALS. We show that blocking IL-10 increased inflammation and precipitated clinical disease onset, whereas overexpression of IL-10 in microglia using a gene therapy approach significantly delayed disease onset and increased survival of ALS mice. Based on our results, we propose that targeted overexpression of IL-10 in microglia may have therapeutic potential in ALS.

Interleukin-6 Deficiency Does Not Affect Motor Neuron Disease Caused by Superoxide Dismutase 1 Mutation

Background & Aim

Amyotrophic Lateral Sclerosis (ALS) is an adult-onset, progressive, motor neuron degenerative disease. Recent evidence indicates that inflammation is associated with many neurodegenerative diseases including ALS. Previously, abnormal levels of inflammatory cytokines including IL-1β, IL-6 and TNF-α were described in ALS patients and/or in mouse ALS models. In addition, one study showed that blocking IL-1β could slow down progression of ALS-like symptoms in mice. In this study, we examined a role for IL-6 in ALS, using an animal model for familial ALS.

Methods

Mice with mutant SOD1 (G93A) transgene, a model for familial ALS, were used in this study. The expression of the major inflammatory cytokines, IL-6, IL-1β and TNF-α, in spinal cords of these SOD1 transgenic (TG) mice were assessed by real time PCR. Mice were then crossed with IL-6(-/-) mice to generate SOD1TG/IL-6(-/-) mice. SOD1 TG/IL-6(-/-) mice (n = 17) were compared with SOD1 TG/IL-6(+/-) mice (n = 18), SOD1 TG/IL-6(+/+) mice (n = 11), WT mice (n = 15), IL-6(+/-) mice (n = 5) and IL-6(-/-) mice (n = 8), with respect to neurological disease severity score, body weight and the survival. We also histologically compared the motor neuron loss in lumber spinal cords and the atrophy of hamstring muscles between these mouse groups.

Results

Levels of IL-6, IL-1β and TNF-α in spinal cords of SOD1 TG mice was increased compared to WT mice. However, SOD1 TG/IL-6(-/-) mice exhibited weight loss, deterioration in motor function and shortened lifespan (167.55 ± 11.52 days), similarly to SOD1 TG /IL-6(+/+) mice (164.31±12.16 days). Motor neuron numbers and IL-1β and TNF-α levels in spinal cords were not significantly different in SOD1 TG /IL-6(-/-) mice and SOD1 TG /IL-6 (+/+) mice.

Conclusion

These results provide compelling preclinical evidence indicating that IL-6 does not directly contribute to motor neuron disease caused by SOD1 mutations.

Innate and adaptive immune responses in the CNS

Almost every disorder of the CNS is said to have an inflammatory component, but the precise nature of inflammation in the CNS is often imprecisely defined, and the role of CNS-resident cells is uncertain compared with that of cells that invade the tissue from the systemic immune compartment. To understand inflammation in the CNS, the term must be better defined, and the response of tissue to disturbances in homoeostasis (eg, neurodegenerative processes) should be distinguished from disorders in which aberrant immune responses lead to CNS dysfunction and tissue destruction (eg, autoimmunity). Whether the inflammatory tissue response to injury is reparative or degenerative seems to be dependent on context and timing, as are the windows of opportunity for therapeutic intervention in inflammatory CNS diseases.

[Neuroinflammation in amyotrophic lateral sclerosis]

Neuroinflammation, characterized by activated astrocytes and microglia, infiltrated T cells, and the subsequent production of inflammatory mediators, is a pathological hallmark of amyotrophic lateral sclerosis (ALS). Since microglia produce proinflammatory cytokines and other neurotoxic or protective molecules and astrocytes reduce their glutamate uptake, these functional changes in glial cells are considered to play important roles in neurodegeneration. However, what regulates the neuroprotective response in neuroinflammation of ALS has not been clarified. In this regard, we identify astrocyte-derived transforming growth factor-β1 (TGF-β1) as a negative regulator of neuroprotective inflammatory response by microglia and T cells. Understanding the pathomechanism of neuroinflammation of ALS leads to the development of new therapies that target glial cells and T cells.

Lack of TNF-alpha receptor type 2 protects motor neurons in a cellular model of amyotrophic lateral sclerosis and in mutant SOD1 mice but does not affect disease progression

Changes in the homeostasis of tumor necrosis factor α (TNFα) have been demonstrated in patients and experimental models of amyotrophic lateral sclerosis (ALS). However, the contribution of TNFα to the development of ALS is still debated. TNFα is expressed by glia and neurons and acts through the membrane receptors TNFR1 and TNFR2, which may have opposite effects in neurodegeneration. We investigated the role of TNFα and its receptors in the selective motor neuron death in ALS in vitro and in vivo. TNFR2 expressed by astrocytes and neurons, but not TNFR1, was implicated in motor neuron loss in primary SOD1-G93A co-cultures. Deleting TNFR2 from SOD1-G93A mice, there was partial but significant protection of spinal motor neurons, sciatic nerves, and tibialis muscles. However, no improvement of motor impairment or survival was observed. Since the sciatic nerves of SOD1-G93A/TNFR2-/- mice showed high phospho-TAR DNA-binding protein 43 (TDP-43) accumulation and low levels of acetyl-tubulin, two indices of axonal dysfunction, the lack of symptom improvement in these mice might be due to impaired function of rescued motor neurons. These results indicate the interaction between TNFR2 and membrane-bound TNFα as an innovative pathway involved in motor neuron death. Nevertheless, its inhibition is not sufficient to stop disease progression in ALS mice, underlining the complexity of this pathology. We show evidence of the involvement of neuronal and astroglial TNFR2 in the motor neuron degeneration in ALS. Both concur to cause motor neuron death in primary astrocyte/spinal neuron co-cultures. TNFR2 deletion partially protects motor neurons and sciatic nerves in SOD1-G93A mice but does not improve their symptoms and survival. However, TNFR2 could be a new target for multi-intervention therapies.

State of the field: An informatics-based systematic review of the SOD1-G93A amyotrophic lateral sclerosis transgenic mouse model

Numerous sub-cellular through system-level disturbances have been identified in over 1300 articles examining the superoxide dismutase-1 guanine 93 to alanine (SOD1-G93A) transgenic mouse amyotrophic lateral sclerosis (ALS) pathophysiology. Manual assessment of such a broad literature base is daunting. We performed a comprehensive informatics-based systematic review or 'field analysis' to agnostically compute and map the current state of the field. Text mining of recaptured articles was used to quantify published data topic breadth and frequency. We constructed a nine-category pathophysiological function-based ontology to systematically organize and quantify the field's primary data. Results demonstrated that the distribution of primary research belonging to each category is: systemic measures an motor function, 59%; inflammation, 46%; cellular energetics, 37%; proteomics, 31%; neural excitability, 22%; apoptosis, 20%; oxidative stress, 18%; aberrant cellular chemistry, 14%; axonal transport, 10%. We constructed a SOD1-G93A field map that visually illustrates and categorizes the 85% most frequently assessed sub-topics. Finally, we present the literature-cited significance of frequently published terms and uncover thinly investigated areas. In conclusion, most articles individually examine at least two categories, which is indicative of the numerous underlying pathophysiological interrelationships. An essential future path is examination of cross-category pathophysiological interrelationships and their co-correspondence to homeostatic regulation and disease progression.

Astrocyte-derived TGF-β1 accelerates disease progression in ALS mice by interfering with the neuroprotective functions of microglia and T cells

Neuroinflammation, which includes both neuroprotective and neurotoxic reactions by activated glial cells and infiltrated immune cells, is involved in the pathomechanism of amyotrophic lateral sclerosis (ALS). However, the cytokines that regulate the neuroprotective inflammatory response in ALS are not clear. Here, we identify transforming growth factor-β1 (TGF-β1), which is upregulated in astrocytes of murine and human ALS, as a negative regulator of neuroprotective inflammatory response. We demonstrate that astrocyte-specific overproduction of TGF-β1 in SOD1(G93A) mice accelerates disease progression in a non-cell-autonomous manner, with reduced IGF-I production in deactivated microglia and fewer T cells with an IFN-γ-dominant milieu. Moreover, expression levels of endogenous TGF-β1 in SOD1(G93A) mice negatively correlate with lifespan. Furthermore, pharmacological administration of a TGF-β signaling inhibitor after disease onset extends survival time of SOD1(G93A) mice. These findings indicate that astrocytic TGF-β1 determines disease progression and is critical to the pathomechanism of ALS.

Protective and Toxic Neuroinflammation in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a clinically heterogeneous disorder characterized by loss of motor neurons, resulting in paralysis and death. Multiple mechanisms of motor neuron injury have been implicated based upon the more than 20 different genetic causes of familial ALS. These inherited mutations compromise diverse motor neuron pathways leading to cell-autonomous injury. In the ALS transgenic mouse models, however, motor neurons do not die alone. Cell death is noncell-autonomous dependent upon a well orchestrated dialogue between motor neurons and surrounding glia and adaptive immune cells. The pathogenesis of ALS consists of 2 stages: an early neuroprotective stage and a later neurotoxic stage. During early phases of disease progression, the immune system is protective with glia and T cells, especially M2 macrophages/microglia, and T helper 2 cells and regulatory T cells, providing anti-inflammatory factors that sustain motor neuron viability. As the disease progresses and motor neuron injury accelerates, a second rapidly progressing phase develops, characterized by M1 macrophages/microglia, and proinflammatory T cells. In rapidly progressing ALS patients, as in transgenic mice, neuroprotective regulatory T cells are significantly decreased and neurotoxicity predominates. Our own therapeutic efforts are focused on modulating these neuroinflammatory pathways. This review will focus on the cellular players involved in neuroinflammation in ALS and current therapeutic strategies to enhance neuroprotection and suppress neurotoxicity with the goal of arresting the progressive and devastating nature of ALS.

Early-stage treatment with Withaferin A reduces levels of misfolded superoxide dismutase 1 and extends lifespan in a mouse model of amyotrophic lateral sclerosis

Approximately 20% of cases of familial amyotrophic lateral sclerosis (ALS) are caused by mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Recent studies have shown that Withaferin A (WA), an inhibitor of nuclear factor-kappa B activity, was efficient in reducing disease phenotype in a TAR DNA binding protein 43 transgenic mouse model of ALS. These findings led us to test WA in mice from 2 transgenic lines expressing different ALS-linked SOD1 mutations, SOD1(G93A) and SOD1(G37R). Intraperitoneal administration of WA at a dosage of 4 mg/kg of body weight was initiated from postnatal day 40 until end stage in SOD1(G93A) mice, and from 9 months until end stage in SOD1(G37R) mice. The beneficial effects of WA in the SOD1(G93A) mice model were accompanied by an alleviation of neuroinflammation, a decrease in levels of misfolded SOD1 species in the spinal cord, and a reduction in loss of motor neurons resulting in delayed disease progression and mortality. Interestingly, WA treatment triggered robust induction of heat shock protein 25 (a mouse ortholog of heat shock protein 27), which may explain the reduced level of misfolded SOD1 species in the spinal cord of SOD1(G93A) mice and the decrease of neuronal injury responses, as revealed by real-time imaging of biophotonic SOD1(G93A) mice expressing a luciferase transgene under the control of the growth-associated protein 43 promoter. These results suggest that WA may represent a potential lead compound for drug development aiming to treat ALS.

The role of the immune system in neurodegenerative disorders: Adaptive or maladaptive?

Neurodegenerative diseases share common features, including catastrophic neuronal loss that leads to cognitive or motor dysfunction. Neuronal injury occurs in an inflammatory milieu that is populated by resident and sometimes, infiltrating, immune cells - all of which participate in a complex interplay between secreted inflammatory modulators and activated immune cell surface receptors. The importance of these immunomodulators is highlighted by the number of immune factors that have been associated with increased risk of neurodegeneration in recent genome-wide association studies. One of the more difficult tasks for designing therapeutic strategies for immune modulation against neurodegenerative diseases is teasing apart beneficial from harmful signals. In this regard, learning more about the immune components of these diseases has yielded common themes. These unifying concepts should eventually enable immune-based therapeutics for treatment of Alzheimer׳s and Parkinson׳s diseases and amyotrophic lateral sclerosis. Targeted immune modulation should be possible to temper maladaptive factors, enabling beneficial immune responses in the context of neurodegenerative diseases. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Tumor necrosis factor alpha: a link between neuroinflammation and excitotoxicity

Tumor necrosis factor alpha (TNF-α) is a proinflammatory cytokine that exerts both homeostatic and pathophysiological roles in the central nervous system. In pathological conditions, microglia release large amounts of TNF-α; this de novo production of TNF-α is an important component of the so-called neuroinflammatory response that is associated with several neurological disorders. In addition, TNF-α can potentiate glutamate-mediated cytotoxicity by two complementary mechanisms: indirectly, by inhibiting glutamate transport on astrocytes, and directly, by rapidly triggering the surface expression of Ca⁺² permeable-AMPA receptors and NMDA receptors, while decreasing inhibitory GABA_A receptors on neurons. Thus, the net effect of TNF-α is to alter the balance of excitation and inhibition resulting in a higher synaptic excitatory/inhibitory ratio. This review summarizes the current knowledge of the cellular and molecular mechanisms by which TNF-α links the neuroinflammatory and excitotoxic processes that occur in several neurodegenerative diseases, but with a special emphasis on amyotrophic lateral sclerosis (ALS). As microglial activation and upregulation of TNF-α expression is a common feature of several CNS diseases, as well as chronic opioid exposure and neuropathic pain, modulating TNF-α signaling may represent a valuable target for intervention.

Microglia induce motor neuron death via the classical NF-κB pathway in amyotrophic lateral sclerosis

Neuroinflammation is one of the most striking hallmarks of amyotrophic lateral sclerosis (ALS). Nuclear factor-kappa B (NF-κB), a master regulator of inflammation, is upregulated in spinal cords of ALS patients and SOD1-G93A mice. In this study, we show that selective NF-κB inhibition in ALS astrocytes is not sufficient to rescue motor neuron (MN) death. However, the localization of NF-κB activity and subsequent deletion of NF-κB signaling in microglia rescued MNs from microglial-mediated death in vitro and extended survival in ALS mice by impairing proinflammatory microglial activation. Conversely, constitutive activation of NF-κB selectively in wild-type microglia induced gliosis and MN death in vitro and in vivo. Taken together, these data provide a mechanism by which microglia induce MN death in ALS and suggest a novel therapeutic target that can be modulated to slow the progression of ALS and possibly other neurodegenerative diseases by which microglial activation plays a role.

Astrocyte toxicity in motor neuron disease: progress and future hopes

ABSTRACT: Motor neuron disease or amyotrophic lateral sclerosis is a complex multicompartmental disorder that belongs to a spectrum of neurodegenerative conditions ranging from pure motor neuron disease to frontotemporal dementia. The symptoms and causes of death are determined by the progressive and relentless loss of motor neurons in the motor cortex and spinal cord, resulting in paralysis and respiratory failure. However, in the past 10 years, compelling evidence has demonstrated that astrocytes are also affected by the disease mechanisms and actively contribute to the neurodegenerative process. This review focuses on the pathways that are dysregulated in astrocytes and how they affect the relationship between astrocytes and motor neurons in amyotrophic lateral sclerosis. Ongoing research using new methodologies to unravel the contribution of specific cell types to the disease are predicted to open the door to new therapeutic interventions to slow disease progression in amyotrophic lateral sclerosis.

Adeno-associated virus-mediated delivery of a recombinant single-chain antibody against misfolded superoxide dismutase for treatment of amyotrophic lateral sclerosis

There is emerging evidence that the misfolding of superoxide dismutase 1 (SOD1) may represent a common pathogenic event in both familial and sporadic amyotrophic lateral sclerosis (ALS). To reduce the burden of misfolded SOD1 species in the nervous system, we have tested a novel therapeutic approach based on adeno-associated virus (AAV)–mediated tonic expression of a DNA construct encoding a secretable single-chain fragment variable (scFv) antibody composed of the variable heavy and light chain regions of a monoclonal antibody (D3H5) binding specifically to misfolded SOD1. A single intrathecal injection of the AAV encoding the single-chain antibody in SOD1^G93A mice at 45 days of age resulted in sustained expression of single-chain antibodies in the spinal cord, and it delayed disease onset and extension of life span by up to 28%, in direct correlation with scFv titers in the spinal cord. The treatment caused attenuation of neuronal stress signals and reduction in levels of misfolded SOD1 in the spinal cord of SOD1^G93A mice. From these results, we propose that an immunotherapy based on intrathecal inoculation of AAV encoding a secretable scFv against misfolded SOD1 should be considered as potential treatment for ALS, especially for individuals carrying SOD1 mutations.

Death Receptors in the Selective Degeneration of Motoneurons in Amyotrophic Lateral Sclerosis

While studies on death receptors have long been restricted to immune cells, the last decade has provided a strong body of evidence for their implication in neuronal death and hence neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS). ALS is a fatal paralytic disorder that primarily affects motoneurons in the brain and spinal cord. A neuroinflammatory process, associated with astrocyte and microglial activation as well as infiltration of immune cells, accompanies motoneuron degeneration and supports the contribution of non-cell-autonomous mechanisms in the disease. Hallmarks of Fas, TNFR, LT-βR, and p75^NTR signaling have been observed in both animal models and ALS patients. This review summarizes to date knowledge of the role of death receptors in ALS and the link existing between the selective loss of motoneurons and neuroinflammation. It further suggests how this recent evidence could be included in an ultimate multiapproach to treat patients.

Eosinophil-derived neurotoxin is elevated in patients with amyotrophic lateral sclerosis

Background and Objectives. Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by loss of motor neurons in the brainstem, motor cortex, and spinal cord. Oxidative stress and neuroinflammation have been implicated in the pathophysiology of ALS. Members of the family of damage-associated molecular patterns, including reactive oxygen species, high-mobility group box 1, and eosinophil-derived neurotoxin (EDN), may participate in pathological conditions. In this study, we aim to discover new biomarker for detecting ALS. Materials and Methods. We examined 44 patients with ALS, 41 patients with Alzheimer's disease, 41 patients with Parkinson's disease, and 44 healthy controls. The concentration of serum EDN was measured using an enzyme-linked immunosorbent assay. Results. EDN levels were significantly increased 2.17-fold in the serum of patients with ALS as compared with healthy controls (P < 0.05). No correlation between the levels of serum EDN and various clinical parameters of ALS was found. Moreover, the levels of serum EDN in patients with Parkinson's disease and Alzheimer's disease and healthy controls were similar. Conclusion. A higher level of serum EDN was found specifically in patients with ALS, indicating that EDN may participate in the pathophysiology of ALS.

Deletion of galectin-3 exacerbates microglial activation and accelerates disease progression and demise in a SOD1(G93A) mouse model of amyotrophic lateral sclerosis

Galectins are pleiotropic carbohydrate-binding lectins involved in inflammation, growth/differentiation, and tissue remodeling. The functional role of galectins in amyotrophic lateral sclerosis (ALS) is unknown. Expression studies revealed increases in galectin-1 mRNA and protein in spinal cords from SOD1(G93A) mice, and in galectin-3 and -9 mRNAs and proteins in spinal cords of both SOD1(G93A) mice and sporadic ALS patients. As the increase in galectin-3 appeared in early presymptomatic stages and increased progressively through to end stage of disease in the mouse, it was selected for additional study, where it was found to be mainly expressed by microglia. Galectin-3 antagonists are not selective and do not readily cross the blood-brain barrier; therefore, we generated SOD1(G93A)/Gal-3(-/-) transgenic mice to evaluate galectin-3 deletion in a widely used mouse model of ALS. Disease progression, neurological symptoms, survival, and inflammation were assessed to determine the effect of galectin-3 deletion on the SOD1(G93A) disease phenotype. Galectin-3 deletion did not change disease onset, but resulted in more rapid progression through functionally defined disease stages, more severely impaired neurological symptoms at all stages of disease, and expiration, on average, 25 days earlier than SOD1(G93A)/Gal-3(+/+) cohorts. In addition, microglial staining, as well as TNF-α, and oxidative injury were increased in SOD1(G93A)/Gal-3(-/-) mice compared with SOD1(G93A)/Gal-3(+/+) cohorts. These data support an important functional role for microglial galectin-3 in neuroinflammation during chronic neurodegenerative disease. We suggest that elevations in galectin-3 by microglia as disease progresses may represent a protective, anti-inflammatory innate immune response to chronic motor neuron degeneration.

TNF-α triggers rapid membrane insertion of Ca(2+) permeable AMPA receptors into adult motor neurons and enhances their susceptibility to slow excitotoxic injury

Excitotoxicity (caused by over-activation of glutamate receptors) and inflammation both contribute to motor neuron (MN) damage in amyotrophic lateral sclerosis (ALS) and other diseases of the spinal cord. Microglial and astrocytic activation in these conditions results in release of inflammatory mediators, including the cytokine, tumor necrosis factor-alpha (TNF-α). TNF-α has complex effects on neurons, one of which is to trigger rapid membrane insertion of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamate receptors, and in some cases, specific insertion of GluA2 lacking, Ca(2+) permeable AMPA receptors (Ca-perm AMPAr). In the present study, we use a histochemical stain based upon kainate stimulated uptake of cobalt ions ("Co(2+) labeling") to provide the first direct demonstration of the presence of substantial numbers of Ca-perm AMPAr in ventral horn MNs of adult rats under basal conditions. We further find that TNF-α exposure causes a rapid increase in the numbers of these receptors, via a phosphatidylinositol 3 kinase (PI3K) and protein kinase A (PKA) dependent mechanism. Finally, to assess the relevance of TNF-α to slow excitotoxic MN injury, we made use of organotypic spinal cord slice cultures. Co(2+) labeling revealed that MNs in these cultures possess Ca-perm AMPAr. Addition of either a low level of TNF-α, or of the glutamate uptake blocker, trans-pyrrolidine-2,4-dicarboxylic acid (PDC) to the cultures for 48 h resulted in little MN injury. However, when combined, TNF-α+PDC caused considerable MN degeneration, which was blocked by the AMPA/kainate receptor blocker, 2,3-Dihydroxy-6-nitro-7-sulfamoylbenzo (F) quinoxaline (NBQX), or the Ca-perm AMPAr selective blocker, 1-naphthyl acetylspermine (NASPM). Thus, these data support the idea that prolonged TNF-α elevation, as may be induced by glial activation, acts in part by increasing the numbers of Ca-perm AMPAr on MNs to enhance injurious excitotoxic effects of deficient astrocytic glutamate transport.

The Role of the Innate Immune System in ALS

Amyotrophic lateral sclerosis (ALS) is a fatal, adult-onset neurodegenerative disease that is characterized by the death of upper and lower motor neurons. Recent studies have made it clear that although motor neurons are the primary targets of the degenerative process, other cell types play key roles in the death of motor neurons. Most notably, cells of the immune system, including astrocytes and microglia have come under increasing scrutiny, after multiple lines of evidence have shown these cells to be deleterious to motor neurons. Both in vitro and in vivo experiments have shown that astrocytes and microglia containing mutated SOD1 are harmful to motor neurons. Several studies on ALS and other neurodegenerative diseases have revealed that reactive astrocytes and microglia are capable of releasing pro-inflammatory factors such as cytokines and chemokines, which are harmful to neighboring neurons. In addition, it is believed that diseased astrocytes can specifically kill motor neurons through the release of toxic factors. Furthermore, in an animal model of the disease, it has been shown that the reduction of SOD1 in microglia may be able to slow the progression of ALS symptoms. Although the exact pathways of motor neuron death in ALS have yet to be elucidated, studies have suggested that they die through aBax-dependent signaling pathway. Mounting evidence suggests that neuroinflammation plays an important role in the degeneration of motor neurons. Based on these findings, anti-inflammatory compounds are currently being tested for their potential to reduce disease severity; however, these studies are only in the preliminary stages. While we understand that astrocytes and microglia play a role in the death of motor neurons in ALS, much work needs to be done to fully understand ALS pathology and the role the immune system plays in disease onset and progression.

Progress in therapy development for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that cannot be slowed substantially using any currently-available clinical tools. Through decades of studying sporadic and familial ALS (SALS and FALS), researchers are coming to understand ALS as a complex syndrome with diverse genetic and environmental etiologies. It is know appreciated that motor neuron degeneration in ALS requires active (gain of function) and passive (loss of function) events to occur in non-neuronal cells, especially astrocytes and microglia. These neuroinflammatory processes produce paracrine factors that detrimentally affect motor neurons, precipitating protein aggregation and compromising cytoskeletal integrity. The result is a loss of neuronal homeostasis and progressive die-back of motor axons culminating in death of the afflicted motor neurons. This review will discuss experimental therapeutics that have been tested in murine ALS models, with an emphasis on those that have progressed to human clinical trials. Reasons will be considered for the frequent failure of preclinical successes to translate into positive clinical outcomes. Finally, this review will explore current trends in experimental therapeutics for ALS with emphasis on the emerging interest in axon guidance signaling pathways as novel targets for pharmacological support of neural cytoskeletal structure and function in order to slow ALS.

The Neuroinflammatory Response in ALS: The Roles of Microglia and T Cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by upper and lower motoneuron death. Mutations in the gene for superoxide dismutase 1 (SOD1) cause a familial form of ALS and have been used to develop transgenic mice which overexpress human mutant SOD1 (mSOD) and these mice exhibit a motoneuron disease which is pathologically and phenotypically similar to ALS. Neuroinflammation is a pathological hallmark of many neurodegenerative diseases including ALS and is typified by the activation and proliferation of microglia and the infiltration of T cells into the brain and spinal cord. Although the neuroinflammatory response has been considered a consequence of neuronal dysfunction and death, evidence indicates that manipulation of this response can alter disease progression. Previously viewed as deleterious to neuronal survival, recent reports suggest a trophic role for activated microglia in the mSOD mouse during the early stages of disease that is dependent on instructive signals from infiltrating T cells. However, at advanced stages of disease, activated microglia acquire increased neurotoxic potential, warranting further investigation into factors capable of skewing microglial activation towards a neurotrophic phenotype as a means of therapeutic intervention in ALS.

Glial-derived prodegenerative signaling in the Drosophila neuromuscular system

We provide evidence for a prodegenerative, glial-derived signaling framework in the Drosophila neuromuscular system that includes caspase and mitochondria-dependent signaling. We demonstrate that Drosophila TNF-α (eiger) is expressed in a subset of peripheral glia, and the TNF-α receptor (TNFR), Wengen, is expressed in motoneurons. NMJ degeneration caused by disruption of the spectrin/ankyrin skeleton is suppressed by an eiger mutation or by eiger knockdown within a subset of peripheral glia. Loss of wengen in motoneurons causes a similar suppression providing evidence for glial-derived prodegenerative TNF-α signaling. Neither JNK nor NFκβ is required for prodegenerative signaling. However, we provide evidence for the involvement of both an initiator and effector caspase, Dronc and Dcp-1, and mitochondrial-dependent signaling. Mutations that deplete the axon and nerve terminal of mitochondria suppress degeneration as do mutations in Drosophila Bcl-2 (debcl), a mitochondria-associated protein, and Apaf-1 (dark), which links mitochondrial signaling with caspase activity in other systems.

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.