Low autophagy capacity implicated in motor system vulnerability to mutant superoxide dismutase

Roflupram alleviates autophagy defects and reduces mutant hSOD1-induced motor neuron damage in cell and mouse models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal and incurable disease involving motor neuron (MN) degeneration and is characterized by ongoing myasthenia and amyotrophia in adults. Most ALS patients die of respiratory muscle paralysis after an average of 3-5 years. Defective autophagy in MNs is considered an important trigger of ALS pathogenesis. Roflupram (ROF) was demonstrated to activate autophagy in microglial cells and exert protective effects against Parkinson's disease (PD) and Alzheimer's disease (AD). Therefore, our research aimed to investigate the efficacy and mechanism of ROF in treating ALS both in vivo and in vitro. We found that ROF could delay disease onset and prolong the survival of hSOD1-G93A transgenic mice. Moreover, ROF protected MNs in the anterior horn of the spinal cord, activated the AMPK/ULK1 signaling pathway, increased autophagic flow, and reduced SOD1 aggregation. In an NSC34 cell line stably transfected with hSOD1-G93A, ROF protected against cellular damage caused by hSOD1-G93A. Moreover, we have demonstrated that ROF inhibited gliosis in ALS model mice. Collectively, our study suggested that ROF is neuroprotective in ALS models and the AMPK/ULK1 signaling pathway is a potential therapeutic target in ALS, which increases autophagic flow and reduces SOD1 aggregation.

Cell-autonomous immune dysfunction driven by disrupted autophagy in C9orf72-ALS iPSC-derived microglia contributes to neurodegeneration

Although microglial activation is widely found in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), the underlying mechanism(s) are poorly understood. Here, using human-induced pluripotent stem cell-derived microglia-like cells (hiPSC-MG) harboring the most common ALS/FTD mutation (C9orf72, mC9-MG), gene-corrected isogenic controls (isoC9-MG), and C9orf72 knockout hiPSC-MG (C9KO-MG), we show that reduced C9ORF72 protein is associated with impaired phagocytosis and an exaggerated immune response upon stimulation with lipopolysaccharide. Analysis of the C9ORF72 interactome revealed that C9ORF72 interacts with regulators of autophagy and functional studies showed impaired initiation of autophagy in mC9-MG and C9KO-MG. Coculture studies with motor neurons (MNs) demonstrated that the autophagy deficit in mC9-MG drives increased vulnerability of mC9-MNs to excitotoxic stimulus. Pharmacological activation of autophagy ameliorated both cell-autonomous functional deficits in hiPSC-MG and MN death in MG-MN coculture. Together, these findings reveal an important role for C9ORF72 in regulating immune homeostasis and identify dysregulation in myeloid cells as a contributor to neurodegeneration in ALS/FTD.

BL-918, a small-molecule activator of ULK1, induces cytoprotective autophagy for amyotrophic lateral sclerosis therapy

Amyotrophic lateral sclerosis (ALS) is one of the most common fatal neurodegenerative diseases in adults. ALS pathogenesis is associated with toxic SOD1 aggregates generated by mutant SOD1. Since autophagy is responsible for the clearance of toxic protein aggregates including SOD1 aggregates, autophagy induction has been considered as a potential strategy for treating ALS. Autophagic signaling is initiated by unc-51 like autophagy activating kinase 1 (ULK1) complex. We previously identified that BL-918 as a specific ULK1 activator, which exerted cytoprotective effect against Parkinson's disease in vitro and in vivo. In this study we investigated whether BL-918 exerted a therapeutic effect against ALS, and characterized its pharmacokinetic profile in rats. In hSODG93A-NSC34 cells, treatment with BL-918 (5, 10 μM) dose-dependently induced ULK1-dependent autophagy, and eliminated toxic SOD1 aggregates. In SODG93A mice, administration of BL-918 (40, 80 mg/kg, b.i.d., i.g.) dose-dependently prolonged lifespan and improved the motor function, and enhanced the clearance of SOD1 aggregates in spinal cord and cerebral cortex through inducing autophagy. In the pharmacokinetic study conducted in rats, we found BL-918 and its 2 metabolites (M8 and M10) present in spinal cord and brain; after intragastric and intravenous administration, BL-918 reached the highest blood concentration compared to M8 and M10. Collectively, ULK1 activator BL-918 displays a therapeutic potential on ALS through inducing cytoprotective autophagy. This study provides a further clue for autophagic dysfunction in ALS pathogenesis.

Mutant SOD1 aggregates formed in vitro and in cultured cells are polymorphic and differ from those arising in the CNS

Mutations in the human Superoxide dismutase 1 (hSOD1) gene are well-established cause of the motor neuron disease ALS. Patients and transgenic (Tg) ALS model mice carrying mutant variants develop hSOD1 aggregates in the CNS. We have identified two hSOD1 aggregate strains, which both transmit spreading template-directed aggregation and premature fatal paralysis when inoculated into adult transgenic mice. This prion-like spread of aggregation could be a primary disease mechanism in SOD1-induced ALS. Human SOD1 aggregation has been studied extensively both in cultured cells and under various conditions in vitro. To determine how the structure of aggregates formed in these model systems related to disease-associated aggregates in the CNS, we used a binary epitope-mapping assay to examine aggregates of hSOD1 variants G93A, G85R, A4V, D90A, and G127X formed in vitro, in four different cell lines and in the CNS of Tg mice. We found considerable variability between replicate sets of in vitro-generated aggregates. In contrast, there was a high similarity between replicates of a given hSOD1 mutant in a given cell line, but pronounced variations between different hSOD1 mutants and different cell lines in both structures and amounts of aggregates formed. The aggregates formed in vitro or in cultured cells did not replicate the aggregate strains that arise in the CNS. Our findings suggest that the distinct aggregate morphologies in the CNS could result from a micro-environment with stringent quality control combined with second-order selection by spreading ability. Explorations of pathogenesis and development of therapeutics should be conducted in models that replicate aggregate structures forming in the CNS.

Targeting the Mitochondrial Protein VDAC1 as a Potential Therapeutic Strategy in ALS

Impaired mitochondrial function has been proposed as a causative factor in neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), caused by motor neuron degeneration. Mutations in superoxide dismutase (SOD1) cause ALS and SOD1 mutants were shown to interact with the voltage-dependent anion channel 1 (VDAC1), affecting its normal function. VDAC1 is a multi-functional channel located at the outer mitochondrial membrane that serves as a mitochondrial gatekeeper controlling metabolic and energetic crosstalk between mitochondria and the rest of the cell and it is a key player in mitochondria-mediated apoptosis. Previously, we showed that VDAC1 interacts with SOD1 and that the VDAC1-N-terminal-derived peptide prevented mutant SOD1 cytotoxic effects. In this study, using a peptide array, we identified the SOD1 sequence that interacts with VDAC1. Synthetic peptides generated from the identified VDAC1-binding sequences in SOD1 directly interacted with purified VDAC1. We also show that VDAC1 oligomerization increased in spinal cord mitochondria isolated from mutant SOD1G93A mice and rats. Thus, we used the novel VDAC1-specific small molecules, VBIT-4 and VBIT-12, inhibiting VDAC1 oligomerization and subsequently apoptosis and associated processes such as ROS production, and increased cytosolic Ca2+. VBIT-12 was able to rescue cell death induced by mutant SOD1 in neuronal cultures. Finally, although survival was not affected, VBIT-12 administration significantly improved muscle endurance in mutant SOD1G93A mice. Therefore, VBIT-12 may represent an attractive therapy for maintaining muscle function during the progression of ALS.

Amyotrophic Lateral Sclerosis and Autophagy: Dysfunction and Therapeutic Targeting

Over the past 20 years, there has been a drastically increased understanding of the genetic basis of Amyotrophic Lateral Sclerosis. Despite the identification of more than 40 different ALS-causing mutations, the accumulation of neurotoxic misfolded proteins, inclusions, and aggregates within motor neurons is the main pathological hallmark in all cases of ALS. These protein aggregates are proposed to disrupt cellular processes and ultimately result in neurodegeneration. One of the main reasons implicated in the accumulation of protein aggregates may be defective autophagy, a highly conserved intracellular "clearance" system delivering misfolded proteins, aggregates, and damaged organelles to lysosomes for degradation. Autophagy is one of the primary stress response mechanisms activated in highly sensitive and specialised neurons following insult to ensure their survival. The upregulation of autophagy through pharmacological autophagy-inducing agents has largely been shown to reduce intracellular protein aggregate levels and disease phenotypes in different in vitro and in vivo models of neurodegenerative diseases. In this review, we explore the intriguing interface between ALS and autophagy, provide a most comprehensive summary of autophagy-targeted drugs that have been examined or are being developed as potential treatments for ALS to date, and discuss potential therapeutic strategies for targeting autophagy in ALS.

The clinical trial landscape in amyotrophic lateral sclerosis-Past, present, and future

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease marked by progressive loss of muscle function. It is the most common adult-onset form of motor neuron disease, affecting about 16 000 people in the United States alone. The average survival is about 3 years. Only two interventional drugs, the antiglutamatergic small-molecule riluzole and the more recent antioxidant edaravone, have been approved for the treatment of ALS to date. Therapeutic strategies under investigation in clinical trials cover a range of different modalities and targets, and more than 70 different drugs have been tested in the clinic to date. Here, we summarize and classify interventional therapeutic strategies based on their molecular targets and phenotypic effects. We also discuss possible reasons for the failure of clinical trials in ALS and highlight emerging preclinical strategies that could provide a breakthrough in the battle against this relentless disease.

Pathomechanism Heterogeneity in the Amyotrophic Lateral Sclerosis and Frontotemporal Dementia Disease Spectrum: Providing Focus Through the Lens of Autophagy

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) constitute aggressive neurodegenerative pathologies that lead to the progressive degeneration of upper and lower motor neurons and of neocortical areas, respectively. In the past decade, the identification of several genes that cause these disorders indicated that the two diseases overlap in a multifaceted spectrum of conditions. The autophagy-lysosome system has been identified as a main intersection for the onset and progression of neurodegeneration in ALS/FTD. Genetic evidence has revealed that several genes with a mechanistic role at different stages of the autophagy process are mutated in patients with ALS/FTD. Moreover, the three main proteins aggregating in ALS/FTD, including in sporadic cases, are also targeted by autophagy and affect this process. Here, we examine the varied dysfunctions and degrees of involvement of the autophagy-lysosome system that have been discovered in ALS/FTD. We argue that these findings shed light on the pathological mechanisms in the ALS/FTD spectrum and conclude that they have important consequences both for treatment options and for the basic biomolecular understanding of how this process intersects with RNA metabolism, the other major cellular process reported to be dysfunctional in part of the ALS/FTD spectrum.

Autophagy as a Cellular Stress Response Mechanism in the Nervous System

Cells of an organism face with various types of insults during their lifetime. Exposure to toxins, metabolic problems, ischaemia/reperfusion, physical trauma, genetic diseases, neurodegenerative diseases are among the conditions that trigger cellular stress responses. In this context, autophagy is one of the mechanisms that supports cell survival under stressful conditions. Autophagic vesicle engulfs the cargo and transports it to lysosome for degradation and turnover. As such, autophagy eliminates abnormal proteins, clears damaged organelles, limits oxidative stress and helps to improve metabolic balance. Nervous system cells and particularly postmitotic neurons are highly sensitive to a spectrum of insults, and autophagy emerges as one of the key stress response mechanism, ensuring health and survival of these vulnerable cell types. In this review, we will overview mechanisms through which cells cope with stress, and how these stress responses regulate autophagy, with a special focus on the nervous system.

Autophagy Induction as a Therapeutic Strategy for Neurodegenerative Diseases

Autophagy is a major, conserved cellular pathway by which cells deliver cytoplasmic contents to lysosomes for degradation. Genetic studies have revealed extensive links between autophagy and neurodegenerative disease, and disruptions to autophagy may contribute to pathology in some cases. Autophagy degrades many of the toxic, aggregate-prone proteins responsible for such diseases, including mutant huntingtin (mHTT), alpha-synuclein (α-syn), tau, and others, raising the possibility that autophagy upregulation may help to reduce levels of toxic protein species, and thereby alleviate disease. This review examines autophagy induction as a potential therapy in several neurodegenerative diseases-Alzheimer's disease, Parkinson's disease, polyglutamine diseases, and amyotrophic lateral sclerosis (ALS). Evidence in cells and in vivo demonstrates promising results in many disease models, in which autophagy upregulation is able to reduce the levels of toxic proteins, ameliorate signs of disease, and delay disease progression. However, the effective therapeutic use of autophagy induction requires detailed knowledge of how the disease affects the autophagy-lysosome pathway, as activating autophagy when the pathway cannot go to completion (e.g., when lysosomal degradation is impaired) may instead exacerbate disease in some cases. Investigating the interactions between autophagy and disease pathogenesis is thus a critical area for further research.

Theme 3 In vitro experimental models

Background: Ongoing disease gene discoveries continue to drive our understanding of the molecular and cellular mechanisms underlying ALS. Causative genes from 60% of ALS families have been identified using modern genetic techniques, but the causal gene defect is yet to be identified in the remaining 40% of families. These remaining families often do not follow true Mendelian inheritance patterns and are challenging to solve using traditional genetic analysis alone. In vitro and in vivo studies have become critical in assessing and validating these ALS candidate genes.Objectives: In this study, we aim to develop and validate the utility of an in vitro functional pipeline for the discovery and validation of novel ALS candidate genes.Methods: A panel of cell based-assays were applied to candidate genes to examine the presence/absence of known ALS pathologies in cell lines as well as human autopsy tissues. These include immunofluorescence, flow cytometry and western blotting to study toxicity, neuronal inclusion formation, interaction with TDP-43, aberrant protein degradation and accumulation in detergent-insoluble cellular fractions. Immunohistochemistry and immunofluorescence were also used to examine if candidates were present in neuronal inclusions from ALS patient spinal cord tissues.Results: The in vitro pipeline was applied to five candidate genes from an ALS family that is negative for known ALS gene mutations. Two candidates were prioritized as top candidates based on their capacity to induce known ALS cellular pathologies. In transfected cells, the variants in these two genes caused a significantly higher toxicity than wild type, formed detergent insoluble inclusions and was able to co-aggregate with TDP-43 in neuronal cells. The variants have also led to protein degradation defects. One of the candidates also co-localised with TDP-43-positive neuronal inclusions in sporadic ALS patient post-mortem tissues, a signature pathology of ALS.Discussion and conclusions: We have demonstrated the utility of a functional prioritization pipeline and successfully prioritized two novel candidate ALS genes. These genes, and its associated pathways, will be further investigated through the development of animal models to establish if there is support for its role in ALS. New ALS genes offer fresh diagnostic and therapeutic targets and tools for the generation of novel animal models to better understand disease biology and offer preclinical testing of candidate treatments for ALS in the future.

[Prion-like Properties of Misfolded Cu/Zn-superoxide Dismutase in Amyotrophic Lateral Sclerosis: Update and Perspectives]

Amyotrophic lateral sclerosis (ALS) is a lethal neurodegenerative disease that is characterized by the loss of motor neurons, which results in progressive muscle atrophy. The pathology spreads from the initial site of onset to contiguous anatomic regions. Mutations in the gene encoding Cu/Zn-superoxide dismutase (SOD1) have been identified in a dominantly inherited form of ALS (ALS-SOD1). A major hallmark of ALS-SOD1 is the abnormal accumulation of conformationally aberrant SOD1 protein (i.e., misfolded SOD1) within motor neurons. Emerging experimental evidence has suggested that misfolded proteins associated with neurodegenerative diseases exhibit prion-like properties, i.e., misfolded proteins act as conformational templates that convert normal proteins into a pathogenic form. Possibly as a result of this prion-like self-propagation property, misfolded forms of pathological proteins are considered to accumulate in the central nervous system and cause neurodegeneration. In this article, we review recent evidence for the role of prion-like mechanisms in ALS-SOD1. In particular, we discuss the propensity of misfolded SOD1 to act as a pathological seed, spread between cells, and propagate neuroanatomically.

SQSTM1/p62: A Potential Target for Neurodegenerative Disease

Neurodegenerative diseases, characterized by a progressive loss of brain function, affect the lives of millions of individuals worldwide. The complexity of the brain poses a challenge for scientists trying to map the biochemical and physiological pathways to identify areas of pathological errors. Brain samples of patients with neurodegenerative diseases have been shown to contain large amounts of misfolded and abnormally aggregated proteins, resulting in dysfunction in certain brain centers. Removal of these abnormal molecules is essential in maintaining protein homeostasis and overall neuronal health. Macroautophagy is a major route by which cells achieve this. Administration of certain autophagy-enhancing compounds has been shown to provide therapeutic effects for individuals with neurodegenerative conditions. SQSTM1/p62 is a scaffold protein closely involved in the macroautophagy process. p62 functions to anchor the ubiquitinated proteins to the autophagosome membrane, promoting degradation of unwanted molecules. Modulators targeting p62 to induce autophagy and promote its protective pathways for aggregate protein clearance have high potential in the treatment of these conditions. Additionally, causal relationships have been found between errors in regulation of SQSTM1/p62 and the development of a variety of neurodegenerative disorders, including Alzheimer's, Parkinson's, Huntington's, amyotrophic lateral sclerosis, and frontotemporal lobar degeneration. Furthermore, SQSTM1/p62 also serves as a signaling hub for multiple pathways associated with neurodegeneration, providing a potential therapeutic target in the treatment of neurodegenerative diseases. However, rational design of a p62-oriented autophagy modulator that can balance the negative and positive functions of multiple domains in p62 requires further efforts in the exploration of the protein structure and pathological basis.

Network approach identifies Pacer as an autophagy protein involved in ALS pathogenesis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a multifactorial fatal motoneuron disease without a cure. Ten percent of ALS cases can be pointed to a clear genetic cause, while the remaining 90% is classified as sporadic. Our study was aimed to uncover new connections within the ALS network through a bioinformatic approach, by which we identified C13orf18, recently named Pacer, as a new component of the autophagic machinery and potentially involved in ALS pathogenesis.

METHODS

Initially, we identified Pacer using a network-based bioinformatic analysis. Expression of Pacer was then investigated in vivo using spinal cord tissue from two ALS mouse models (SOD1^G93A and TDP43^A315T) and sporadic ALS patients. Mechanistic studies were performed in cell culture using the mouse motoneuron cell line NSC34. Loss of function of Pacer was achieved by knockdown using short-hairpin constructs. The effect of Pacer repression was investigated in the context of autophagy, SOD1 aggregation, and neuronal death.

RESULTS

Using an unbiased network-based approach, we integrated all available ALS data to identify new functional interactions involved in ALS pathogenesis. We found that Pacer associates to an ALS-specific subnetwork composed of components of the autophagy pathway, one of the main cellular processes affected in the disease. Interestingly, we found that Pacer levels are significantly reduced in spinal cord tissue from sporadic ALS patients and in tissues from two ALS mouse models. In vitro, Pacer deficiency lead to impaired autophagy and accumulation of ALS-associated protein aggregates, which correlated with the induction of cell death.

CONCLUSIONS

This study, therefore, identifies Pacer as a new regulator of proteostasis associated with ALS pathology.

Heterozygous Tbk1 loss has opposing effects in early and late stages of ALS in mice

Heterozygous loss-of-function mutations of TANK-binding kinase 1 (TBK1 ) cause familial ALS, yet downstream mechanisms of TBK1 mutations remained elusive. TBK1 is a pleiotropic kinase involved in the regulation of selective autophagy and inflammation. We show that heterozygous Tbk1 deletion alone does not lead to signs of motoneuron degeneration or disturbed autophagy in mice during a 200-d observation period. Surprisingly, however, hemizygous deletion of Tbk1 inversely modulates early and late disease phases in mice additionally overexpressing ALS-linked SOD1G93A , which represents a "second hit" that induces both neuroinflammation and proteostatic dysregulation. At the early stage, heterozygous Tbk1 deletion impairs autophagy in motoneurons and prepones both the clinical onset and muscular denervation in SOD1G93A/Tbk1+/- mice. At the late disease stage, however, it significantly alleviates microglial neuroinflammation, decelerates disease progression, and extends survival. Our results indicate a profound effect of TBK1 on brain inflammatory cells under pro-inflammatory conditions and point to a complex, two-edged role of TBK1 in SOD1-linked ALS.

24-Epibrassinolide-alleviated drought stress damage influences antioxidant enzymes and autophagy changes in peach (Prunus persicae L.) leaves

Drought stress is a serious threat to agriculture and the environment. Brassinosteroids (BRs) increase tolerance to drought stress of plant. Autophagy plays important roles in plant responses to drought stress; however, there are few reports on autophagy in peach (Prunus persica). In total, 23 putative autophagy-related genes (ATGs) in peach were identified using ATGs from the Arabidopsis thaliana genome as query in BLASTx algorithm-based searches. Under drought stress, the photosynthetic abilities of peach leaves decreased, while antioxidant enzyme activities, autophagy and ATG expression increased. A correlation analysis showed that antioxidant enzyme activities are inversely correlated to the expression levels of the PpATGs. During drought, the PpATG8s and some PpATG18s had the strongest responses. To investigate enhanced drought-stress tolerance, peach was treated with water, 100 nM 24-epibrassinolide (EBR), 1 μM EBR, 10 μM EBR and 1 μM voriconazole. Exogenous EBR at 1 μM decreased the malondialdehyde (MDA) content under drought stress when compared with water-, 1 μM voriconazole-, 100 nM EBR- and 10 μM EBR-treated peach leaf. The 1-μM EBR application increased superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione peroxidase (GR) activities during drought stress. In addition, the expression levels of PpATGs were inhibited by EBR. Thus, the 1-μM EBR treatment alleviated drought-stress damage to peach leaves, decreased PpATG expression levels and reduced the number of autophagosomes.

Mutant superoxide dismutase aggregates from human spinal cord transmit amyotrophic lateral sclerosis

Motor neurons containing aggregates of superoxide dismutase 1 (SOD1) are hallmarks of amyotrophic lateral sclerosis (ALS) caused by mutations in the gene encoding SOD1. We have previously reported that two strains of mutant human (h) SOD1 aggregates (denoted A and B) can arise in hSOD1-transgenic models for ALS and that inoculation of such aggregates into the lumbar spinal cord of mice results in rostrally spreading, templated hSOD1 aggregation and premature fatal ALS-like disease. Here, we explored whether mutant hSOD1 aggregates with prion-like properties also exist in human ALS. Aggregate seeds were prepared from spinal cords from an ALS patient carrying the hSOD1^G127Gfs*7 truncation mutation and from mice transgenic for the same mutation. To separate from mono-, di- or any oligomeric hSOD1 species, the seed preparation protocol included ultracentrifugation through a density cushion. The core structure of hSOD1^G127Gfs*7 aggregates present in mice was strain A-like. Inoculation of the patient- or mouse-derived seeds into lumbar spinal cord of adult hSOD1-expressing mice induced strain A aggregation propagating along the neuraxis and premature fatal ALS-like disease (p < 0.0001). Inoculation of human or murine control seeds had no effect. The potencies of the ALS patient-derived seed preparations were high and disease was initiated in the transgenic mice by levels of hSOD1^G127Gfs*7 aggregates much lower than those found in the motor system of patients carrying the mutation. The results suggest that prion-like growth and spread of hSOD1 aggregation could be the primary pathogenic mechanism, not only in hSOD1 transgenic rodent models, but also in human ALS.

Autophagy and lysosomal pathways in nervous system disorders

Autophagy is an evolutionarily conserved pathway for delivering cytoplasmic cargo to lysosomes for degradation. In its classically studied form, autophagy is a stress response induced by starvation to recycle building blocks for essential cellular processes. In addition, autophagy maintains basal cellular homeostasis by degrading endogenous substrates such as cytoplasmic proteins, protein aggregates, damaged organelles, as well as exogenous substrates such as bacteria and viruses. Given their important role in homeostasis, autophagy and lysosomal machinery are genetically linked to multiple human disorders such as chronic inflammatory diseases, cardiomyopathies, cancer, and neurodegenerative diseases. Multiple targets within the autophagy and lysosomal pathways offer therapeutic opportunities to benefit patients with these disorders. Here, I will summarize the mechanisms of autophagy pathways, the evidence supporting a pathogenic role for disturbed autophagy and lysosomal degradation in nervous system disorders, and the therapeutic potential of autophagy modulators in the clinic.

Repurposing carbamazepine for the treatment of amyotrophic lateral sclerosis in SOD1-G93A mouse model

AIMS

To investigate the effect and mechanisms of carbamazepine (CBZ) on the onset and progression of amyotrophic lateral sclerosis (ALS) in SOD1-G93A mouse model.

METHODS

Starting from 64 days of age, SOD1-G93A mice were orally administered with CBZ at 200 mg/kg once daily until death. The disease onset and life span of SOD1-G93A mice were recorded. Motor neurons (MNs) in anterior horn of spinal cord were quantified by Nissl staining and SMI-32 immunostaining. Hematoxylin and eosin (H&E), nicotinamide adenine dinucleotide hydrogen (NADH), modified Gomori trichrome (MGT), and α-bungarotoxin-ATTO-488 staining were also performed to evaluate muscle and neuromuscular junction (NMJ) damage. Expressions of aggregated SOD1 protein and autophagy-related proteins were further detected by Western blot and immunofluorescent staining.

RESULTS

Carbamazepine treatment could delay the disease onset and extend life span of SOD1-G93A mice by about 14.5% and 13.9%, respectively. Furthermore, CBZ treatment reduced MNs loss by about 46.6% and ameliorated the altered muscle morphology and NMJ. Much more interestingly, mechanism study revealed that CBZ treatment activated autophagy via AMPK-ULK1 pathway and promoted the clearance of mutant SOD1 aggregation.

CONCLUSION

Our findings uncovered the therapeutic effects of CBZ against disease pathogenesis in SOD1-G93A mice, indicating a promising clinical utilization of CBZ in ALS therapy.

A copper-deficient form of mutant Cu/Zn-superoxide dismutase as an early pathological species in amyotrophic lateral sclerosis

Dominant mutations in the gene encoding copper and zinc-binding superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS). Abnormal accumulation of misfolded SOD1 proteins in spinal motoneurons is a major pathological hallmark in SOD1-related ALS. Dissociation of copper and/or zinc ions from SOD1 has been shown to trigger the protein aggregation/oligomerization in vitro, but the pathological contribution of such metal dissociation to the SOD1 misfolding still remains obscure. Here, we tested the relevance of the metal-deficient SOD1 in the misfolding in vivo by developing a novel antibody (anti-apoSOD), which exclusively recognized mutant SOD1 deficient in metal ions at its copper-binding site. Notably, anti-apoSOD-reactive species were detected specifically in the spinal cords of the ALS model mice only at their early pre-symptomatic stages but not at the end stage of the disease. The cerebrospinal fluid as well as the spinal cord homogenate of one SOD1-ALS patient also contained the anti-apoSOD-reactive species. Our results thus suggest that metal-deficiency in mutant SOD1 at its copper-binding site is one of the earliest pathological features in SOD1-ALS.

Unraveling the role of motoneuron autophagy in ALS

In recent years, the role of autophagy in the pathogenesis of most neurodegenerative diseases has transitioned into a limbo of protective or detrimental effects. Genetic evidence indicates that mutations in autophagy-regulatory genes can result in the occurrence of amyotrophic lateral sclerosis (ALS), suggesting a physiological role of the pathway to motoneuron function. However, experimental manipulation of autophagy in ALS models led to conflicting results depending on the intervention strategy and the disease model used. A recent work by the Maniatis group systematically explored the role of cell-specific autophagy in motoneurons at different disease stages, revealing surprising and unexpected findings. Autophagy activity at early stages may contribute to maintaining the structure and function of neuromuscular junctions, whereas at later steps of the disease it has a pathogenic activity possibly involving cell-nonautonomous mechanisms related to glial activation. This new study adds a new layer of complexity in the field, suggesting an intricate interplay between proteostasis alterations, the time-differential function of autophagy in neurons, and muscle innervation in ALS.

Proteostasis disturbance in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting motoneurons in the brain and spinal cord leading to paralysis and death. Although the etiology of ALS remains poorly understood, abnormal protein aggregation and altered proteostasis are common features of sporadic and familial ALS forms. The proteostasis network is decomposed into different modules highly conserved across species and comprehends a collection of mechanisms related to protein synthesis, folding, trafficking, secretion and degradation that is distributed in different compartments inside the cell. Functional studies in various ALS models are revealing a complex scenario where distinct and even opposite effects in disease progression are observed depending on the targeted component of the proteostasis network. Importantly, alteration of the folding capacity of the endoplasmic reticulum (ER) is becoming a common pathological alteration in ALS, representing one of the earliest defects observed in disease models, contributing to denervation and motoneuron dysfunction. Strategies to target-specific components of the proteostasis network using small molecules and gene therapy are under development, and promise interesting avenues for future interventions to delay or stop ALS progression.

Autophagy Dysregulation in ALS: When Protein Aggregates Get Out of Hand

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that results from the loss of upper and lower motor neurons. One of the key pathological hallmarks in diseased neurons is the mislocalization of disease-associated proteins and the formation of cytoplasmic aggregates of these proteins and their interactors due to defective protein quality control. This apparent imbalance in the cellular protein homeostasis could be a crucial factor in causing motor neuron death in the later stages of the disease in patients. Autophagy is a major protein degradation pathway that is involved in the clearance of protein aggregates and damaged organelles. Abnormalities in autophagy have been observed in numerous neurodegenerative disorders, including ALS. In this review, we discuss the contribution of autophagy dysfunction in various in vitro and in vivo models of ALS. Furthermore, we examine the crosstalk between autophagy and other cellular stresses implicated in ALS pathogenesis and the therapeutic implications of regulating autophagy in ALS.

Protein Homeostasis in Amyotrophic Lateral Sclerosis: Therapeutic Opportunities?

Protein homeostasis (proteostasis), the correct balance between production and degradation of proteins, is essential for the health and survival of cells. Proteostasis requires an intricate network of protein quality control pathways (the proteostasis network) that work to prevent protein aggregation and maintain proteome health throughout the lifespan of the cell. Collapse of proteostasis has been implicated in the etiology of a number of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), the most common adult onset motor neuron disorder. Here, we review the evidence linking dysfunctional proteostasis to the etiology of ALS and discuss how ALS-associated insults affect the proteostasis network. Finally, we discuss the potential therapeutic benefit of proteostasis network modulation in ALS.

Neurodegeneration and NLRP3 inflammasome expression in the anterior thalamus of SOD1(G93A) ALS mice

Nowadays, amyotrophic lateral sclerosis (ALS) is considered as a multisystem disorder, characterized by a primary degeneration of motor neurons as well as neuropathological changes in non-motor regions. Neurodegeneration in subcortical areas, such as the thalamus, are believed to contribute to cognitive and behavioral abnormalities in ALS patients. In the present study, we investigated neurodegenerative changes including neuronal loss and glia pathology in the anterodorsal thalamic nucleus (AD) of SOD1(G93A) mice, a widely used animal model for ALS. We detected massive dendrite swelling and neuronal loss in SOD1(G93A) animals, which was accompanied by a mild gliosis. Furthermore, misfolded SOD1 protein and autophagy markers were accumulating in the AD. Since innate immunity and activation inflammasomes seem to play a crucial role in ALS, we examined protein expression of Nod-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein containing a caspase-1 recruitment domain (ASC) and the cytokine interleukin 1 beta (IL1β) in AD glial cells and neurons. NLRP3 and ASC were significantly up-regulated in the AD of SOD1(G93A) mice. Finally, co-localization studies revealed expression of NLRP3, ASC and IL1β in neurons. Our study yielded two main findings: (i) neurodegenerative changes already occur at an early symptomatic stage in the AD and (ii) increased inflammasome expression may contribute to neuronal cell death. In conclusion, neurodegeneration in the anterior thalamus may critically account for cognitive changes in ALS pathology.

Necroptosis in amyotrophic lateral sclerosis and other neurological disorders

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the progressive degeneration of upper and lower motor neurons. Cell death in ALS and in general was previously believed to exist as a dichotomy between apoptosis and necrosis. Most research investigating cell death mechanisms in ALS was conducted before the discovery of programmed necrosis thus did not use selective cell death pathway-specific markers. Recently, a new form of programmed cell death, termed "necroptosis", has been characterized and has been recently implicated in ALS as a primary mechanism driving motor neuron cell death in different forms of ALS. The present review is aimed at summarizing cell death pathways that are currently implicated in ALS and highlighting the emerging evidence on necroptosis as a major driver of motor neuron cell death.

Transcription Factor EB Is Selectively Reduced in the Nuclear Fractions of Alzheimer's and Amyotrophic Lateral Sclerosis Brains

Multiple studies suggest that autophagy is strongly dysregulated in Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), as evidenced by accumulation of numerous autophagosomes, lysosomes with discontinuous membranes, and aggregated proteins in the patients' brains. Transcription factor EB (TFEB) was recently discovered to be a master regulator of lysosome biogenesis and autophagy. To examine whether aberrant autophagy in AD and ALS is due to alterations in TFEB expression, we systematically quantified the levels of TFEB in these brains by immunoblotting. Interestingly, cytoplasmic fractions of AD brains showed increased levels of normalized (to tubulin) TFEB only at Braak stage IV (61%, p < 0.01). Most importantly, normalized (to lamin) TFEB levels in the nuclear fractions were consistently reduced starting from Braak stage IV (52%, p < 0.01), stage V (67%, p < 0.01), and stage VI (85%, p < 0.01) when compared to normal control (NC) brains. In the ALS brains also, nuclear TFEB levels were reduced by 62% (p < 0.001). These data suggest that nuclear TFEB is selectively lost in ALS as well as AD brains, in which TFEB reduction was Braak-stage-dependent. Taken together, the observed reductions in TFEB protein levels may be responsible for the widely reported autophagy defects in these disorders.

Two superoxide dismutase prion strains transmit amyotrophic lateral sclerosis-like disease

Amyotrophic lateral sclerosis (ALS) is an adult-onset degeneration of motor neurons that is commonly caused by mutations in the gene encoding superoxide dismutase 1 (SOD1). Both patients and Tg mice expressing mutant human SOD1 (hSOD1) develop aggregates of unknown importance. In Tg mice, 2 different strains of hSOD1 aggregates (denoted A and B) can arise; however, the role of these aggregates in disease pathogenesis has not been fully characterized. Here, minute amounts of strain A and B hSOD1 aggregate seeds that were prepared by centrifugation through a density cushion were inoculated into lumbar spinal cords of 100-day-old mice carrying a human SOD1 Tg. Mice seeded with A or B aggregates developed premature signs of ALS and became terminally ill after approximately 100 days, which is 200 days earlier than for mice that had not been inoculated or were given a control preparation. Concomitantly, exponentially growing strain A and B hSOD1 aggregations propagated rostrally throughout the spinal cord and brainstem. The phenotypes provoked by the A and B strains differed regarding progression rates, distribution, end-stage aggregate levels, and histopathology. Together, our data indicate that the aggregate strains are prions that transmit a templated, spreading aggregation of hSOD1, resulting in a fatal ALS-like disease.

Proteostasis impairment in ALS

In physiological conditions the maintenance of the cellular proteome is a prerequisite for optimal cell functioning and cell survival. Additionally, cells need to constantly sense and adapt to their changing environment and associated stressors. Cells achieve this via a set of molecular chaperones, protein clearance pathways as well as stress-associated signaling networks which work together to prevent protein misfolding, its aggregation and accumulation in subcellular compartments. These processes together form the proteostasis network which helps in maintaining cellular proteostasis. Imbalance or impairment in this processes is directly linked to ageing associated disorders such as diabetes, cancer, stroke, metabolic disorders, pulmonary fibrosis, inflammation and neurodegenerative diseases. In this review, we provide insights into the proteostasis process and how its failure governs neurodegenerative disorders with a special focus on Amyotrophic lateral sclerosis (ALS). This article is part of a Special Issue entitled SI:ER stress.