Skeletal Muscle in ALS: An Unappreciated Therapeutic Opportunity?

Urolithin a Improves Motor Dysfunction Induced by Copper Exposure in SOD1G93A Transgenic Mice Via Activation of Mitophagy

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease pathologically characterized by selective degeneration of motor neurons resulting in a catastrophic loss of motor function. The present study aimed to investigate the effect of copper (Cu) exposure on progression of ALS and explore the therapeutic effect and mechanism of Urolithin A (UA) on ALS. 0.13 PPM copper chloride drinking water was administrated in SOD1G93A transgenic mice at 6 weeks, UA at a dosage of 50 mg/kg/day was given for 6 weeks after a 7-week Cu exposure. Motor ability was assessed before terminal anesthesia. Muscle atrophy and fibrosis, motor neurons, astrocytes and microglia in the spinal cord were evaluated by H&E, Masson, Sirius Red, Nissl and Immunohistochemistry Staining. Proteomics analysis, Western blotting and ELISA were conducted to detect protein expression. Mitochondrial adenosine triphosphate (ATP) and malondialdehyde (MDA) levels were measured using an assay kit. Cu-exposure worsened motor function, promoted muscle fibrosis, loss of motor neurons, and astrocyte and microglial activation. It also induced abnormal changes in mitochondria-related biological processes, leading to a significant reduction in ATP levels and an increase in MDA levels. Upregulation of P62 and downregulation of Parkin, PINK1, and LAMP1 were revealed in SOD1G93A mice with Cu exposure. Administration of UA activated mitophagy, modulated mitochondria dysfunction, reduced neuroinflammation, and improved gastrocnemius muscle atrophy and motor dysfunction in SOD1G93A mice with Cu exposure. Mitophagy plays critical role in ALS exacerbated by Cu exposure. UA administration may be a promising treatment strategy for ALS.

Dysregulated FOXO1 activity drives skeletal muscle intrinsic dysfunction in amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a multisystemic neurodegenerative disorder, with accumulating evidence indicating metabolic disruptions in the skeletal muscle preceding disease symptoms, rather than them manifesting as a secondary consequence of motor neuron (MN) degeneration. Hence, energy homeostasis is deeply implicated in the complex physiopathology of ALS and skeletal muscle has emerged as a key therapeutic target. Here, we describe intrinsic abnormalities in ALS skeletal muscle, both in patient-derived muscle cells and in muscle cell lines with genetic knockdown of genes related to familial ALS, such as TARDBP (TDP-43) and FUS. We found a functional impairment of myogenesis that parallels defects of glucose oxidation in ALS muscle cells. We identified FOXO1 transcription factor as a key mediator of these metabolic and functional features in ALS muscle, via gene expression profiling and biochemical surveys in TDP-43 and FUS-silenced muscle progenitors. Strikingly, inhibition of FOXO1 mitigated the impaired myogenesis in both the genetically modified and the primary ALS myoblasts. In addition, specific in vivo conditional knockdown of TDP-43 or FUS orthologs (TBPH or caz) in Drosophila muscle precursor cells resulted in decreased innervation and profound dysfunction of motor nerve terminals and neuromuscular synapses, accompanied by motor abnormalities and reduced lifespan. Remarkably, these phenotypes were partially corrected by foxo inhibition, bolstering the potential pharmacological management of muscle intrinsic abnormalities associated with ALS. The findings demonstrate an intrinsic muscle dysfunction in ALS, which can be modulated by targeting FOXO factors, paving the way for novel therapeutic approaches that focus on the skeletal muscle as complementary target tissue.

Testosterone Reduces Myelin Abnormalities in the Wobbler Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motoneuron degenerative disease that is associated with demyelination. The Wobbler (WR) mouse exhibits motoneuron degeneration, gliosis and myelin deterioration in the cervical spinal cord. Since male WRs display low testosterone (T) levels in the nervous system, we investigated if T modified myelin-relative parameters in WRs in the absence or presence of the aromatase inhibitor, anastrozole (A). We studied myelin by using luxol-fast-blue (LFB) staining, semithin sections, electron microscopy and myelin protein expression, density of IBA1+ microglia and mRNA expression of inflammatory factors, and the glutamatergic parameters glutamine synthetase (GS) and the transporter GLT1. Controls and WR + T showed higher LFB, MBP and PLP staining, lower g-ratios and compact myelin than WRs and WR + T + A, and groups showing the rupture of myelin lamellae. WRs showed increased IBA1+ cells and mRNA for CD11b and inflammatory factors (IL-18, TLR4, TNFαR1 and P2Y12R) vs. controls or WR + T. IBA1+ cells, and CD11b were not reduced in WR + T + A, but inflammatory factors' mRNA remained low. A reduction of GS+ cells and GLT-1 immunoreactivity was observed in WRs and WR + T + A vs. controls and WR + T. Clinically, WR + T but not WR + T + A showed enhanced muscle mass, grip strength and reduced paw abnormalities. Therefore, T effects involve myelin protection, a finding of potential clinical translation.

Neuromuscular organoids model spinal neuromuscular pathologies in C9orf72 amyotrophic lateral sclerosis

Hexanucleotide repeat expansions in the C9orf72 gene are the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. Due to the lack of trunk neuromuscular organoids (NMOs) from ALS patients' induced pluripotent stem cells (iPSCs), an organoid system was missing to model the trunk spinal neuromuscular neurodegeneration. With the C9orf72 ALS patient-derived iPSCs and isogenic controls, we used an NMO system containing trunk spinal cord neural and peripheral muscular tissues to show that the ALS NMOs could model peripheral defects in ALS, including contraction weakness, neural denervation, and loss of Schwann cells. The neurons and astrocytes in ALS NMOs manifested the RNA foci and dipeptide repeat proteins. Acute treatment with the unfolded protein response inhibitor GSK2606414 increased the glutamatergic muscular contraction 2-fold and reduced the dipeptide repeat protein aggregation and autophagy. This study provides an organoid system for spinal neuromuscular pathologies in ALS and its application for drug testing.

Endurance exercise has a negative impact on the onset of SOD1-G93A ALS in female mice and affects the entire skeletal muscle-motor neuron axis

Background

Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disease characterized by the degeneration of motor neurons that leads to muscle wasting and atrophy. Epidemiological and experimental evidence suggests a causal relationship between ALS and physical activity (PA). However, the impact of PA on motor neuron loss and sarcopenia is still debated, probably because of the heterogeneity and intensities of the proposed exercises. With this study, we aimed to clarify the effect of intense endurance exercise on the onset and progression of ALS in the SOD1-G93A mouse model.

Methods

We randomly selected four groups of twelve 35-day-old female mice. SOD1-G93A and WT mice underwent intense endurance training on a motorized treadmill for 8 weeks, 5 days a week. During the training, we measured muscle strength, weight, and motor skills and compared them with the corresponding sedentary groups to define the disease onset. At the end of the eighth week, we analyzed the skeletal muscle-motor neuron axis by histological and molecular techniques.

Results

Intense endurance exercise anticipates the onset of the disease by 1 week (age of the onset: trained SOD1-G93A = 63.17 ± 2.25 days old; sedentary SOD1-G93A = 70.75 ± 2.45 days old). In SOD1-G93A mice, intense endurance exercise hastens the muscular switch to a more oxidative phenotype and worsens the denervation process by dismantling neuromuscular junctions in the tibialis anterior, enhancing the Wallerian degeneration in the sciatic nerve, and promoting motor neuron loss in the spinal cord. The training exacerbates neuroinflammation, causing immune cell infiltration in the sciatic nerve and a faster activation of astrocytes and microglia in the spinal cord.

Conclusion

Intense endurance exercise, acting on skeletal muscles, worsens the pathological hallmarks of ALS, such as denervation and neuroinflammation, brings the onset forward, and accelerates the progression of the disease. Our findings show the potentiality of skeletal muscle as a target for both prognostic and therapeutic strategies; the preservation of skeletal muscle health by specific intervention could counteract the dying-back process and protect motor neurons from death. The physiological characteristics and accessibility of skeletal muscle further enhance its appeal as a therapeutic target.

Progressive Irreversible Proprioceptive Piezo2 Channelopathy-Induced Lost Forced Peripheral Oscillatory Synchronization to the Hippocampal Oscillator May Explain the Onset of Amyotrophic Lateral Sclerosis Pathomechanism

Amyotrophic lateral sclerosis (ALS) is a mysterious lethal multisystem neurodegenerative disease that gradually leads to the progressive loss of motor neurons. A recent non-contact dying-back injury mechanism theory for ALS proposed that the primary damage is an acquired irreversible intrafusal proprioceptive terminal Piezo2 channelopathy with underlying genetic and environmental risk factors. Underpinning this is the theory that excessively prolonged proprioceptive mechanotransduction under allostasis may induce dysfunctionality in mitochondria, leading to Piezo2 channelopathy. This microinjury is suggested to provide one gateway from physiology to pathophysiology. The chronic, but not irreversible, form of this Piezo2 channelopathy is implicated in many diseases with unknown etiology. Dry eye disease is one of them where replenishing synthetic proteoglycans promote nerve regeneration. Syndecans, especially syndecan-3, are proposed as the first critical link in this hierarchical ordered depletory pathomechanism as proton-collecting/distributing antennas; hence, they may play a role in ALS pathomechanism onset. Even more importantly, the shedding or charge-altering variants of Syndecan-3 may contribute to the Piezo2 channelopathy-induced disruption of the Piezo2-initiated proton-based ultrafast long-range signaling through VGLUT1 and VGLUT2. Thus, these alterations may not only cause disruption to ultrafast signaling to the hippocampus in conscious proprioception, but could disrupt the ultrafast proprioceptive signaling feedback to the motoneurons. Correspondingly, an inert Piezo2-initiated proton-based ultrafast signaled proprioceptive skeletal system is coming to light that is suggested to be progressively lost in ALS. In addition, the lost functional link of the MyoD family of inhibitor proteins, as auxiliary subunits of Piezo2, may not only contribute to the theorized acquired Piezo2 channelopathy, but may explain how these microinjured ion channels evolve to be principal transcription activators.

Functional consequences of familial ALS-associated SOD1L84F in neuronal and muscle cells

Amyotrophic lateral sclerosis is a fatal neurodegenerative disorder characterized by progressive skeletal muscle denervation and loss of motor neurons that results in muscle atrophy and eventual death due to respiratory failure. Previously, we identified a novel SOD1L84F variation in a familial ALS case. In this study, we examined the functional consequences of SOD1L84F overexpression in the mouse motor neuron cell line (NSC-34). The cells expressing SOD1L84F showed increased oxidative stress and increased cell death. Interestingly, SOD1L84F destabilized the native dimer and formed high molecular weight SDS-resistant protein aggregates. Furthermore, SOD1L84F also decreased the percentage of differentiated cells and significantly reduced neurite length. A plethora of evidence suggested active involvement of skeletal muscle in disease initiation and progression. We observed differential processing of the mutant SOD1 and perturbations of cellular machinery in NSC-34 and muscle cell line C2C12. Unlike neuronal cells, mutant protein failed to accumulate in muscle cells probably due to the activated autophagy, as evidenced by increased LC3-II and reduced p62. Further, SOD1L84F altered mitochondrial dynamics only in NSC-34. In addition, microarray analysis also revealed huge variations in differentially expressed genes between NSC-34 and C2C12. Interestingly, SOD1L84F hampered the endogenous FUS autoregulatory mechanism in NSC-34 by downregulating retention of introns 6 and 7 resulting in a two-fold upregulation of FUS. No such changes were observed in C2C12. Our findings strongly suggest the differential processing and response towards the mutant SOD1 in neuronal and muscle cell lines.

An optogenetic cell therapy to restore control of target muscles in an aggressive mouse model of amyotrophic lateral sclerosis

Breakdown of neuromuscular junctions (NMJs) is an early pathological hallmark of amyotrophic lateral sclerosis (ALS) that blocks neuromuscular transmission, leading to muscle weakness, paralysis and, ultimately, premature death. Currently, no therapies exist that can prevent progressive motor neuron degeneration, muscle denervation, or paralysis in ALS. Here, we report important advances in the development of an optogenetic, neural replacement strategy that can effectively restore innervation of severely affected skeletal muscles in the aggressive SOD1G93A mouse model of ALS, thus providing an interface to selectively control the function of targeted muscles using optical stimulation. We also identify a specific approach to confer complete survival of allogeneic replacement motor neurons. Furthermore, we demonstrate that an optical stimulation training paradigm can prevent atrophy of reinnervated muscle fibers and results in a tenfold increase in optically evoked contractile force. Together, these advances pave the way for an assistive therapy that could benefit all ALS patients.

Scalable, optically-responsive human neuromuscular junction model reveals convergent mechanisms of synaptic dysfunction in familial ALS

Neuromuscular junctions (NMJs) are specialized synapses that mediate communication between motor neurons and skeletal muscles and are essential for movement. The degeneration of this system can lead to symptoms observed in neuromuscular and motor neuron diseases. Studying these synapses and their degeneration has proven challenging. Prior NMJ studies heavily relied upon the use of mouse, chick, or isolated primary human cells, which have demonstrated limited fidelity for disease modeling. To enable the study of NMJ dysfunction and model genetic diseases, we, and others, have developed methods to generate human NMJs from pluripotent stem cells (PSCs), embryonic stem cells, and induced pluripotent stem cells. However, published studies have highlighted technical limitations associated with these complex in vitro NMJ models. In this study, we developed a robust PSC-derived motor neuron and skeletal muscle co-culture method, and demonstrated its sensitivity in modeling motor neuron disease. Our method spontaneously and reproducibly forms human NMJs. We developed multiwell-multielectrode array (MEA) parameters to quantify the activity of PSC-derived skeletal muscles, as well as measured the electrophysiological activity of functional human PSC-derived NMJs. We further leveraged our method to morphologically and functionally assess NMJs from the familial amyotrophic lateral sclerosis (fALS) PSCs, C9orf72 hexanucleotide (G4C2)n repeat expansion (HRE), SOD1 A5V , and TDP43 G298S to define the reproducibility and sensitivity of our system. We observed a significant decrease in the numbers and activity of PSC-derived NMJs developed from the different ALS lines compared to their respective controls. Furthermore, we evaluated a therapeutic candidate undergoing clinical trials and observed a variant-dependent rescue of functionality of NMJs. Our newly developed method provides a platform for the systematic investigation of genetic causes of NMJ neurodegeneration and highlights the need for therapeutic avenues to consider patient genotype.

Effect of the Mediterranean diet supplemented with nicotinamide riboside and pterostilbene and/or coconut oil on anthropometric variables in amyotrophic lateral sclerosis. A pilot study

Amyotrophic Lateral Sclerosis (ALS) is a chronic and progressive neurodegenerative disease that causes the death of motor neurons and alters patients' body composition. Supplementation with the antioxidants nicotinamide riboside (NR) and pterostilbene (PTER) can combat associated oxidative stress. Additionally, coconut oil is an alternative energy substrate that can address mitochondrial dysfunction. The aim of the present study is to assess the impact of a Mediterranean Diet supplemented with NR and PTER and/or with coconut oil on the anthropometric variables of patients with ALS. A prospective, mixed, randomized, analytical and experimental pilot study in humans was performed through a clinical trial (registered with ClinicalTrials.gov under number NCT03489200) with pre- and post-intervention assessments. The sample was made up of 40 subjects categorized into four study groups (Control, Antioxidants, Coconut oil, and Antioxidants + Coconut oil). Pre- and post-intervention anthropometric assessments were carried out to determine the following data: weight, percentage of fat and muscle mass, skinfolds, body perimeters, Body Mass Index (BMI), Waste-to-Hip Index (WHI) and Waist-Height Ratio (WHR). Compared to the Control group, GAx significantly increased muscle mass percentage and decreased fat mass percentage, triceps, iliac crest, and abdominal skinfolds. GCoco significantly increased muscle mass percentage and decreased fat mass percentage, subscapular skinfolds, and abdominal skinfolds. GAx + coco significantly increased muscle mass percentage and decreased abdominal skinfolds. Therefore, our results suggest that the Mediterranean Diet supplemented with NR and PTER and the Mediterranean Diet supplemented with coconut oil (ketogenic diet) are the two nutritional interventions that have reported the greatest benefits, at anthropometric level.

Altered Metabolism in Motor Neuron Diseases: Mechanism and Potential Therapeutic Target

Motor Neuron Diseases (MND) are neurological disorders characterized by a loss of varying motor neurons resulting in decreased physical capabilities. Current research is focused on hindering disease progression by determining causes of motor neuron death. Metabolic malfunction has been proposed as a promising topic when targeting motor neuron loss. Alterations in metabolism have also been noted at the neuromuscular junction (NMJ) and skeletal muscle tissue, emphasizing the importance of a cohesive system. Finding metabolism changes consistent throughout both neurons and skeletal muscle tissue could pose as a target for therapeutic intervention. This review will focus on metabolic deficits reported in MNDs and propose potential therapeutic targets for future intervention.

Intramuscular IL-10 Administration Enhances the Activity of Myogenic Precursor Cells and Improves Motor Function in ALS Mouse Model

Amyotrophic Lateral Sclerosis (ALS) is the most common adult motor neuron disease, with a poor prognosis, a highly unmet therapeutic need, and a burden on health care costs. Hitherto, strategies aimed at protecting motor neurons have missed or modestly delayed ALS due to a failure in countering the irreversible muscular atrophy. We recently provided direct evidence underlying the pivotal role of macrophages in preserving skeletal muscle mass. Based on these results, we explored whether the modulation of macrophage muscle response and the enhancement of satellite cell differentiation could effectively promote the generation of new myofibers and counteract muscle dysfunction in ALS mice. For this purpose, disease progression and the survival of SOD1G93A mice were evaluated following IL-10 injections in the hindlimb skeletal muscles. Thereafter, we used ex vivo methodologies and in vitro approaches on primary cells to assess the effect of the treatment on the main pathological signatures. We found that IL-10 improved the motor performance of ALS mice by enhancing satellite cells and the muscle pro-regenerative activity of macrophages. This resulted in delayed muscle atrophy and motor neuron loss. Our findings provide the basis for a suitable adjunct multisystem therapeutic approach that pinpoints a primary role of muscle pathology in ALS.

Immune-mediated myogenesis and acetylcholine receptor clustering promote a slow disease progression in ALS mouse models

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a heterogeneous disease in terms of onset and progression rate. This may account for therapeutic clinical trial failure. Transgenic SOD1G93A mice on C57 or 129Sv background have a slow and fast disease progression rate, mimicking the variability observed in patients. Based on evidence inferring the active influence of skeletal muscle on ALS pathogenesis, we explored whether dysregulation in hindlimb skeletal muscle reflects the phenotypic difference between the two mouse models.

METHODS

Ex vivo immunohistochemical, biochemical, and biomolecular methodologies, together with in vivo electrophysiology and in vitro approaches on primary cells, were used to afford a comparative and longitudinal analysis of gastrocnemius medialis between fast- and slow-progressing ALS mice.

RESULTS

We reported that slow-progressing mice counteracted muscle denervation atrophy by increasing acetylcholine receptor clustering, enhancing evoked currents, and preserving compound muscle action potential. This matched with prompt and sustained myogenesis, likely triggered by an early inflammatory response switching the infiltrated macrophages towards a M2 pro-regenerative phenotype. Conversely, upon denervation, fast-progressing mice failed to promptly activate a compensatory muscle response, exhibiting a rapidly progressive deterioration of muscle force.

CONCLUSIONS

Our findings further pinpoint the pivotal role of skeletal muscle in ALS, providing new insights into underestimated disease mechanisms occurring at the periphery and providing useful (diagnostic, prognostic, and mechanistic) information to facilitate the translation of cost-effective therapeutic strategies from the laboratory to the clinic.

Sporadic Spinal-Onset Amyotrophic Lateral Sclerosis Associated with Myopathy in Three Unrelated Portuguese Patients

Amyotrophic lateral sclerosis (ALS) and myopathy have been already described as part of a common genetic syndrome called multisystem proteinopathy. They may occur together or not, and can be associated with other clinical features such as frontotemporal dementia and Paget's bone disease. In addition, primary skeletal muscle involvement has been also reported in inherited forms of lower motor neuron disease, in spinal-bulbar muscular atrophy and in spinal muscular atrophy. We aim to characterize three sporadic, spinal-onset ALS patients, one with a concurrent non-specific myopathy, and two with a previous diagnosis of myopathy before upper and lower motor neuron signs emerged. Perhaps our sporadic ALS cases associated with myopathy share a common, but still unknown, pathogenic background. These cases raise the paradigm of a possible interplay between skeletal muscle degeneration and motor neuron damage.

Upper and Lower Motor Neurons and the Skeletal Muscle: Implication for Amyotrophic Lateral Sclerosis (ALS)

The relationships between motor neurons and the skeletal muscle during development and in pathologic contexts are addressed in this Chapter.We discuss the developmental interplay of muscle and nervous tissue, through neurotrophins and the activation of differentiation and survival pathways. After a brief overview on muscular regulatory factors, we focus on the contribution of muscle to early and late neurodevelopment. Such a role seems especially intriguing in relation to the epigenetic shaping of developing motor neuron fate choices. In this context, emphasis is attributed to factors regulating energy metabolism, which may concomitantly act in muscle and neural cells, being involved in common pathways.We then review the main features of motor neuron diseases, addressing the cellular processes underlying clinical symptoms. The involvement of different muscle-associated neurotrophic factors for survival of lateral motor column neurons, innervating MyoD-dependent limb muscles, and of medial motor column neurons, innervating Myf5-dependent back musculature is discussed. Among the pathogenic mechanisms, we focus on oxidative stress, that represents a common and early trait in several neurodegenerative disorders. The role of organelles primarily involved in reactive oxygen species scavenging and, more generally, in energy metabolism-namely mitochondria and peroxisomes-is discussed in the frame of motor neuron degeneration.We finally address muscular involvement in amyotrophic lateral sclerosis (ALS), a multifactorial degenerative disorder, hallmarked by severe weight loss, caused by imbalanced lipid metabolism. Even though multiple mechanisms have been recognized to play a role in the disease, current literature generally assumes that the primum movens is neuronal degeneration and that muscle atrophy is only a consequence of such pathogenic event. However, several lines of evidence point to the muscle as primarily involved in the disease, mainly through its role in energy homeostasis. Data from different ALS mouse models strongly argue for an early mitochondrial dysfunction in muscle tissue, possibly leading to motor neuron disturbances. Detailed understanding of skeletal muscle contribution to ALS pathogenesis will likely lead to the identification of novel therapeutic strategies.

2021 Editor's Choice Articles in the Section "Cells of the Nervous System"

Referenced below are the top 10 cited papers in 2021 from the Section "Cells of the Nervous System", published in Cells (ISSN: 2073-4409) [...].

The Cellular and Molecular Signature of ALS in Muscle

Amyotrophic lateral sclerosis is a disease affecting upper and lower motor neurons. Although motor neuron death is the core event of ALS pathology, it is increasingly recognized that other tissues and cell types are affected in the disease, making potentially major contributions to the occurrence and progression of pathology. We review here the known cellular and molecular characteristics of muscle tissue affected by ALS. Evidence of toxicity in skeletal muscle tissue is considered, including metabolic dysfunctions, impaired proteostasis, and deficits in muscle regeneration and RNA metabolism. The role of muscle as a secretory organ, and effects on the skeletal muscle secretome are also covered, including the increase in secretion of toxic factors or decrease in essential factors that have consequences for neuronal function and survival.

Deciphering lipid dysregulation in ALS: from mechanisms to translational medicine

Lipids, defined by low solubility in water and high solubility in nonpolar solvents, can be classified into fatty acids, glycerolipids, glycerophospholipids, sphingolipids, and sterols. Lipids not only regulate integrity and fluidity of biological membranes, but also serve as energy storage and bioactive molecules for signaling. Causal mutations in SPTLC1 (serine palmitoyltransferase long chain subunit 1) gene within the lipogenic pathway have been identified in amyotrophic lateral sclerosis (ALS), a paralytic and fatal motor neuron disease. Furthermore, lipid dysmetabolism within the central nervous system and circulation is associated with ALS. Here, we aim to delineate the diverse roles of different lipid classes and understand how lipid dysmetabolism may contribute to ALS pathogenesis. Among the different lipids, accumulation of ceramides, arachidonic acid, and lysophosphatidylcholine is commonly emerging  as detrimental to motor neurons. We end with exploring the potential ALS therapeutics by reducing these toxic lipids.

Deficient Sarcolemma Repair in ALS: A Novel Mechanism with Therapeutic Potential

The plasma membrane (sarcolemma) of skeletal muscle myofibers is susceptible to injury caused by physical and chemical stresses during normal daily movement and/or under disease conditions. These acute plasma membrane disruptions are normally compensated by an intrinsic membrane resealing process involving interactions of multiple intracellular proteins including dysferlin, annexin, caveolin, and Mitsugumin 53 (MG53)/TRIM72. There is new evidence for compromised muscle sarcolemma repair mechanisms in Amyotrophic Lateral Sclerosis (ALS). Mitochondrial dysfunction in proximity to neuromuscular junctions (NMJs) increases oxidative stress, triggering MG53 aggregation and loss of its function. Compromised membrane repair further worsens sarcolemma fragility and amplifies oxidative stress in a vicious cycle. This article is to review existing literature supporting the concept that ALS is a disease of oxidative-stress induced disruption of muscle membrane repair that compromise the integrity of the NMJs and hence augmenting muscle membrane repair mechanisms could represent a viable therapeutic strategy for ALS.

The Impact of Spermidine on C2C12 Myoblasts Proliferation, Redox Status and Polyamines Metabolism under H2O2 Exposure

A central feature of the skeletal muscle is its ability to regenerate through the activation, by environmental signals, of satellite cells. Once activated, these cells proliferate as myoblasts, and defects in this process profoundly affect the subsequent process of regeneration. High levels of reactive oxygen species such as hydrogen peroxide (H₂O₂) with the consequent formation of oxidized macromolecules increase myoblasts’ cell death and strongly contribute to the loss of myoblast function. Recently, particular interest has turned towards the beneficial effects on muscle of the naturally occurring polyamine spermidine (Spd). In this work, we tested the hypothesis that Spd, upon oxidative challenge, would restore the compromised myoblasts’ viability and redox status. The effects of Spd in combination with aminoguanidine (Spd-AG), an inhibitor of bovine serum amine oxidase, on murine C2C12 myoblasts treated with a mild dose of H₂O₂ were evaluated by analyzing: (i) myoblast viability and recovery from wound scratch; (ii) redox status and (iii) polyamine (PAs) metabolism. The treatment of C2C12 myoblasts with Spd-AG increased cell number and accelerated scratch wound closure, while H₂O₂ exposure caused redox status imbalance and cell death. The combined treatment with Spd-AG showed an antioxidant effect on C2C12 myoblasts, partially restoring cellular total antioxidant capacity, reducing the oxidized glutathione (GSH/GSSG) ratio and increasing cell viability through a reduction in cell death. Moreover, Spd-AG administration counteracted the induction of polyamine catabolic genes and PA content decreased due to H₂O₂ challenges. In conclusion, our data suggest that Spd treatment has a protective role in skeletal muscle cells by restoring redox balance and promoting recovery from wound scratches, thus making myoblasts able to better cope with an oxidative insult.

New Insights into the Neurodegeneration Mechanisms Underlying Riboflavin Transporter Deficiency (RTD): Involvement of Energy Dysmetabolism and Cytoskeletal Derangement

Riboflavin transporter deficiency (RTD) is a rare genetic disorder characterized by motor, sensory and cranial neuropathy. This childhood-onset neurodegenerative disease is caused by biallelic pathogenic variants in either SLC52A2 or SLC52A3 genes, resulting in insufficient supply of riboflavin (vitamin B2) and consequent impairment of flavoprotein-dependent metabolic pathways. Current therapy, empirically based high-dose riboflavin supplementation, ameliorates the progression of the disease, even though response to treatment is variable and partial. Recent studies have highlighted concurrent pathogenic contribution of cellular energy dysmetabolism and cytoskeletal derangement. In this context, patient specific RTD models, based on induced pluripotent stem cell (iPSC) technology, have provided evidence of redox imbalance, involving mitochondrial and peroxisomal dysfunction. Such oxidative stress condition likely causes cytoskeletal perturbation, associated with impaired differentiation of RTD motor neurons. In this review, we discuss the most recent findings obtained using different RTD models. Relevantly, the integration of data from innovative iPSC-derived in vitro models and invertebrate in vivo models may provide essential information on RTD pathophysiology. Such novel insights are expected to suggest custom therapeutic strategies, especially for those patients unresponsive to high-dose riboflavin treatments.

TAR DNA-binding protein of 43 kDa (TDP-43) and amyotrophic lateral sclerosis (ALS): a promising therapeutic target

INTRODUCTION

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease that lacks an effective treatment. Aggregates of the TAR DNA-binding protein-43 (TDP-43) are observed in 97% of all ALS cases, thus making this protein a major therapeutic target in ALS. .

AREAS COVERED

The authors describe the major cellular functions of TDP-43 and the features and consequences of TDP-43 proteinopathy. Drawing from fundamental and preclinical studies on cellular and animal TDP-43 models of ALS and selected clinical trials, the major pathways that have been targeted for the mitigation of TDP-43 pathology in ALS are discussed. The authors provide insights on the approaches targeting the tendency of TDP-43 for aggregation, defective nucleocytoplasmic transport, dysfunctional proteostasis, abnormal stress granule dynamics, and pathological post-translational modifications of TDP-43.

EXPERT OPINION

The complexity of ALS and TDP-43 proteinopathy generates challenges for the development of novel therapeutic approaches. However, the critical involvement of TDP-43 in the initiation and progression of ALS, makes it a promising therapeutic target. Further research should be centered on the development of precision strategies, consideration of patient subgroups, the prevention of the mislocalization of TDP-43 and restoration of the lost functions of TPD-43. .

Mechanistic Insights of Mitochondrial Dysfunction in Amyotrophic Lateral Sclerosis: An Update on a Lasting Relationship

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of the upper and lower motor neurons. Despite the increasing effort in understanding the etiopathology of ALS, it still remains an obscure disease, and no therapies are currently available to halt its progression. Following the discovery of the first gene associated with familial forms of ALS, Cu–Zn superoxide dismutase, it appeared evident that mitochondria were key elements in the onset of the pathology. However, as more and more ALS-related genes were discovered, the attention shifted from mitochondria impairment to other biological functions such as protein aggregation and RNA metabolism. In recent years, mitochondria have again earned central, mechanistic roles in the pathology, due to accumulating evidence of their derangement in ALS animal models and patients, often resulting in the dysregulation of the energetic metabolism. In this review, we first provide an update of the last lustrum on the molecular mechanisms by which the most well-known ALS-related proteins affect mitochondrial functions and cellular bioenergetics. Next, we focus on evidence gathered from human specimens and advance the concept of a cellular-specific mitochondrial “metabolic threshold”, which may appear pivotal in ALS pathogenesis.

Comprehensive Research on Past and Future Therapeutic Strategies Devoted to Treatment of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly debilitating fatal neurodegenerative disorder, causing muscle atrophy and weakness, which leads to paralysis and eventual death. ALS has a multifaceted nature affected by many pathological mechanisms, including oxidative stress (also via protein aggregation), mitochondrial dysfunction, glutamate-induced excitotoxicity, apoptosis, neuroinflammation, axonal degeneration, skeletal muscle deterioration and viruses. This complexity is a major obstacle in defeating ALS. At present, riluzole and edaravone are the only drugs that have passed clinical trials for the treatment of ALS, notwithstanding that they showed modest benefits in a limited population of ALS. A dextromethorphan hydrobromide and quinidine sulfate combination was also approved to treat pseudobulbar affect (PBA) in the course of ALS. Globally, there is a struggle to prevent or alleviate the symptoms of this neurodegenerative disease, including implementation of antisense oligonucleotides (ASOs), induced pluripotent stem cells (iPSCs), CRISPR-9/Cas technique, non-invasive brain stimulation (NIBS) or ALS-on-a-chip technology. Additionally, researchers have synthesized and screened new compounds to be effective in ALS beyond the drug repurposing strategy. Despite all these efforts, ALS treatment is largely limited to palliative care, and there is a strong need for new therapeutics to be developed. This review focuses on and discusses which therapeutic strategies have been followed so far and what can be done in the future for the treatment of ALS.

The Contribution of Non-Neuronal Cells in Neurodegeneration: From Molecular Pathogenesis to Therapeutic Challenges

Neuron loss occurring in neurodegenerative diseases represents just the final step in a series of events involving several cell types, other than neurons, that actively contribute to the overall pathogenic mechanisms by establishing harmful non-cell autonomous effects [...].

The acute muscular response following a novel form of pulsed direct current stimulation (Neubie) or traditional resistance exercise

OBJECTIVES

To examine changes in muscle thickness (MT), soreness (SOR), and isometric torque (ISO) following exercise with pulsed direct current (Neubie) or traditional high-load (TRAD) exercise.

METHODS

Thirty-two participants had SOR, MT, and ISO measured before, immediately after, and 24 and 48h following TRAD and Neubie. Rating of perceived exertion (RPE) and discomfort were also measured. Results are displayed as means(SD).

RESULTS

For MT, there was a condition x time interaction (p<0.001). For Neubie, MT increased pre [3.7(0.7)cm] to post [3.9(0.8) cm, p<0.001] and remained elevated at 24h. For TRAD, MT increased pre [3.7(0.6)cm] to post [4.0 (0.7)cm, p<0.001] and remained up to 48h. Greater values were observed for TRAD post-exercise. For ISO, both conditions decreased up to 48h. TRAD demonstrated a greater change post exercise (p<0.001). For SOR, both conditions increased up to 48h. Neubie demonstrated greater SOR at 48h (p=0.007). RPE was higher for all sets in TRAD [Mean across sets=16.0(1.9) vs. 13.5(2), p<0.001]. Discomfort was higher in all sets for Neubie [Mean across sets=5.8(1.5)vs. 4.5(2.0), p<0.05].

CONCLUSIONS

Both conditions showed increased SOR, and decreased ISO for up to 48h, with MT increased for up to 24h. MT remained elevated in TRAD at 48h. Neubie training might be effective for individuals who are looking to experience lower RPE responses during exercise.

Contingent intramuscular boosting of P2XR7 axis improves motor function in transgenic ALS mice

Amyotrophic lateral sclerosis is a fatal neurodegenerative disorder that leads to progressive degeneration of motor neurons and severe muscle atrophy without effective treatment. Most research on the disease has been focused on studying motor neurons and supporting cells of the central nervous system. Strikingly, the recent observations have suggested that morpho-functional alterations in skeletal muscle precede motor neuron degeneration, bolstering the interest in studying muscle tissue as a potential target for the delivery of therapies. We previously showed that the systemic administration of the P2XR7 agonist, 2′(3′)-O‐(4-benzoylbenzoyl) adenosine 5-triphosphate (BzATP), enhanced the metabolism and promoted the myogenesis of new fibres in the skeletal muscles of SOD1G93A mice. Here we further corroborated this evidence showing that intramuscular administration of BzATP improved the motor performance of ALS mice by enhancing satellite cells and the muscle pro-regenerative activity of infiltrating macrophages. The preservation of the skeletal muscle retrogradely propagated along with the motor unit, suggesting that backward signalling from the muscle could impinge on motor neuron death. In addition to providing the basis for a suitable adjunct multisystem therapeutic approach in ALS, these data point out that the muscle should be at the centre of ALS research as a target tissue to address novel therapies in combination with those oriented to the CNS.

Repurposing of Trimetazidine for Amyotrophic Lateral Sclerosis: a study in SOD1G93A mice

Background and Purpose

Amyotrophic lateral sclerosis (ALS), a neurodegenerative disease characterized by the degeneration of upper and lower motor neurons, progressive wasting and paralysis of voluntary muscles and is currently incurable. Although considered to be a pure motor neuron disease, increasing evidence indicates that the sole protection of motor neurons by a single targeted drug is not sufficient to improve the pathological phenotype. We therefore evaluated the therapeutic potential of the multi‐target drug used to treatment of coronary artery disease, trimetazidine, in SOD1^G93A mice.

Experimental Approach

As a metabolic modulator, trimetazidine improves glucose metabolism. Furthermore, trimetazidine enhances mitochondrial metabolism and promotes nerve regeneration, exerting an anti‐inflammatory and antioxidant effect. We orally treated SOD1^G93A mice with trimetazidine, solubilized in drinking water at a dose of 20 mg kg⁻¹, from disease onset. We assessed the impact of trimetazidine on disease progression by studying metabolic parameters, grip strength and histological alterations in skeletal muscle, peripheral nerves and the spinal cord.

Key Results

Trimetazidine administration delays motor function decline, improves muscle performance and metabolism, and significantly extends overall survival of SOD1^G93A mice (increased median survival of 16 days and 12.5 days for male and female respectively). Moreover, trimetazidine prevents the degeneration of neuromuscular junctions, attenuates motor neuron loss and reduces neuroinflammation in the spinal cord and in peripheral nerves.

Conclusion and Implications

In SOD1^G93A mice, therapeutic effect of trimetazidine is underpinned by its action on mitochondrial function in skeletal muscle and spinal cord.

All Roads Lead to Rome: Different Molecular Players Converge to Common Toxic Pathways in Neurodegeneration

Multiple neurodegenerative diseases (NDDs) such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington’s disease (HD) are being suggested to have common cellular and molecular pathological mechanisms, characterized mainly by protein misfolding and aggregation. These large inclusions, most likely, represent an end stage of a molecular cascade; however, the soluble misfolded proteins, which take part in earlier steps of this cascade, are the more toxic players. These pathological proteins, which characterize each specific disease, lead to the selective vulnerability of different neurons, likely resulting from a combination of different intracellular mechanisms, including mitochondrial dysfunction, ER stress, proteasome inhibition, excitotoxicity, oxidative damage, defects in nucleocytoplasmic transport, defective axonal transport and neuroinflammation. Damage within these neurons is enhanced by damage from the nonneuronal cells, via inflammatory processes that accelerate the progression of these diseases. In this review, while acknowledging the hallmark proteins which characterize the most common NDDs; we place specific focus on the common overlapping mechanisms leading to disease pathology despite these different molecular players and discuss how this convergence may occur, with the ultimate hope that therapies effective in one disease may successfully translate to another.

Mitogen-Activated Protein Kinase Pathway in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis is a fatal motor neuron degenerative disease. Multiple genetic and non-genetic risk factors are associated with disease pathogenesis, and several cellular processes, including protein homeostasis, RNA metabolism, vesicle transport, etc., are severely impaired in ALS conditions. Despite the heterogeneity of the disease manifestation and progression, ALS patients show protein aggregates in the motor cortex and spinal cord tissue, which is believed to be at least partially caused by aberrant phase separation and the formation of persistent stress granules. Consistent with this notion, many studies have implicated cellular stress, such as ER stress, DNA damage, oxidative stress, and growth factor depletion, in ALS conditions. The mitogen-activated protein kinase (MAPK) pathway is a fundamental mitogen/stress-activated signal transduction pathway that regulates cell proliferation, differentiation, survival, and death. Here we summarize the fundamental role of MAPK in physiology and ALS pathogenesis. We also discuss pharmacological inhibitors targeting this pathway tested in pre-clinical models, suggesting their role as potential drug candidates.

Protein Aggregation Landscape in Neurodegenerative Diseases: Clinical Relevance and Future Applications

Intrinsic disorder is a natural feature of polypeptide chains, resulting in the lack of a defined three-dimensional structure. Conformational changes in intrinsically disordered regions of a protein lead to unstable β-sheet enriched intermediates, which are stabilized by intermolecular interactions with other β-sheet enriched molecules, producing stable proteinaceous aggregates. Upon misfolding, several pathways may be undertaken depending on the composition of the amino acidic string and the surrounding environment, leading to different structures. Accumulating evidence is suggesting that the conformational state of a protein may initiate signalling pathways involved both in pathology and physiology. In this review, we will summarize the heterogeneity of structures that are produced from intrinsically disordered protein domains and highlight the routes that lead to the formation of physiological liquid droplets as well as pathogenic aggregates. The most common proteins found in aggregates in neurodegenerative diseases and their structural variability will be addressed. We will further evaluate the clinical relevance and future applications of the study of the structural heterogeneity of protein aggregates, which may aid the understanding of the phenotypic diversity observed in neurodegenerative disorders.

Role of Matricellular CCN Proteins in Skeletal Muscle: Focus on CCN2/CTGF and Its Regulation by Vasoactive Peptides

The Cellular Communication Network (CCN) family of matricellular proteins comprises six proteins that share conserved structural features and play numerous biological roles. These proteins can interact with several receptors or soluble proteins, regulating cell signaling pathways in various tissues under physiological and pathological conditions. In the skeletal muscle of mammals, most of the six CCN family members are expressed during embryonic development or in adulthood. Their roles during the adult stage are related to the regulation of muscle mass and regeneration, maintaining vascularization, and the modulation of skeletal muscle fibrosis. This work reviews the CCNs proteins' role in skeletal muscle physiology and disease, focusing on skeletal muscle fibrosis and its regulation by Connective Tissue Growth factor (CCN2/CTGF). Furthermore, we review evidence on the modulation of fibrosis and CCN2/CTGF by the renin-angiotensin system and the kallikrein-kinin system of vasoactive peptides.

Where and Why Modeling Amyotrophic Lateral Sclerosis

Over the years, researchers have leveraged a host of different in vivo models in order to dissect amyotrophic lateral sclerosis (ALS), a neurodegenerative/neuroinflammatory disease that is heterogeneous in its clinical presentation and is multigenic, multifactorial and non-cell autonomous. These models include both vertebrates and invertebrates such as yeast, worms, flies, zebrafish, mice, rats, guinea pigs, dogs and, more recently, non-human primates. Despite their obvious differences and peculiarities, only the concurrent and comparative analysis of these various systems will allow the untangling of the causes and mechanisms of ALS for finally obtaining new efficacious therapeutics. However, harnessing these powerful organisms poses numerous challenges. In this context, we present here an updated and comprehensive review of how eukaryotic unicellular and multicellular organisms that reproduce a few of the main clinical features of the disease have helped in ALS research to dissect the pathological pathways of the disease insurgence and progression. We describe common features as well as discrepancies among these models, highlighting new insights and emerging roles for experimental organisms in ALS.