Muscle Expression of SOD1G93A Triggers the Dismantlement of Neuromuscular Junction via PKC-Theta

Research progress on astrocyte-derived extracellular vesicles in the pathogenesis and treatment of neurodegenerative diseases

Neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), pose significant global health risks and represent a substantial public health concern in the contemporary era. A primary factor in the pathophysiology of these disorders is aberrant accumulation and aggregation of pathogenic proteins within the brain and spinal cord. Recent investigations have identified extracellular vesicles (EVs) in the central nervous system (CNS) as potential carriers for intercellular transport of misfolded proteins associated with neurodegenerative diseases. EVs are involved in pathological processes that contribute to various brain disorders including neurodegenerative disorders. Proteins linked to neurodegenerative disorders are secreted and distributed from cell to cell via EVs, serving as a mechanism for direct intercellular communication through the transfer of biomolecules. Astrocytes, as active participants in CNS intercellular communication, release astrocyte-derived extracellular vesicles (ADEVs) that are capable of interacting with diverse target cells. This review primarily focuses on the involvement of ADEVs in the development of neurological disorders and explores their potential dual roles - both advantageous and disadvantageous in the context of neurological disorders. Furthermore, this review examines the current studies investigating ADEVs as potential biomarkers for the diagnosis and treatment of neurodegenerative diseases. The prospects and challenges associated with the application of ADEVs in clinical settings were also comprehensively reviewed.

Skeletal muscle dysfunction in amyotrophic lateral sclerosis: a mitochondrial perspective and therapeutic approaches

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neuromuscular disease that results in the loss of motor neurons and severe skeletal muscle atrophy. The etiology of ALS is linked to skeletal muscle, which can activate a retrograde signaling cascade that destroys motor neurons. This is why satellite cells and mitochondria play a crucial role in the health and performance of skeletal muscles. This review presents current knowledge on the involvement of mitochondrial dysfunction, skeletal muscle atrophy, muscle satellite cells, and neuromuscular junction (NMJ) in ALS. It also discusses current therapeutic strategies, including exercise, drugs, stem cells, gene therapy, and the prospective use of mitochondrial transplantation as a viable therapeutic strategy.

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.

Unraveling the causes of sarcopenia: Roles of neuromuscular junction impairment and mitochondrial dysfunction

Sarcopenia is a systemic skeletal muscle disease characterized by a decline in skeletal muscle mass and function. Originally defined as an age-associated condition, sarcopenia presently also encompasses muscular atrophy due to various pathological factors, such as intensive care unit-acquired weakness, inactivity, and malnutrition. The exact pathogenesis of sarcopenia is still unknown; herein, we review the pathological roles of the neuromuscular junction and mitochondria in this condition. Sarcopenia is caused by complex and interdependent pathophysiological mechanisms, including aging, neuromuscular junction impairment, mitochondrial dysfunction, insulin resistance, lipotoxicity, endocrine factors, oxidative stress, and inflammation. Among these, neuromuscular junction instability and mitochondrial dysfunction are particularly significant. Dysfunction in neuromuscular junction can lead to muscle weakness or paralysis. Mitochondria, which are plentiful in neurons and muscle fibers, play an important role in neuromuscular junction transmission. Therefore, impairments in both mitochondria and neuromuscular junction may be one of the key pathophysiological mechanisms leading to sarcopenia. Moreover, this article explores the structural and functional alterations in the neuromuscular junction and mitochondria in sarcopenia, suggesting that a deeper understanding of these changes could provide valuable insights for the prevention or treatment of sarcopenia.

Skeletal muscle in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), the major adult-onset motor neuron disease, has been viewed almost exclusively as a disease of upper and lower motor neurons, with muscle changes interpreted as a consequence of the progressive loss of motor neurons and neuromuscular junctions. This has led to the prevailing view that the involvement of muscle in ALS is only secondary to motor neuron loss. Skeletal muscle and motor neurons reciprocally influence their respective development and constitute a single functional unit. In ALS, multiple studies indicate that skeletal muscle dysfunction might contribute to progressive muscle weakness, as well as to the final demise of neuromuscular junctions and motor neurons. Furthermore, skeletal muscle has been shown to participate in disease pathogenesis of several monogenic diseases closely related to ALS. Here, we move the narrative towards a better appreciation of muscle as a contributor of disease in ALS. We review the various potential roles of skeletal muscle cells in ALS, from passive bystanders to active players in ALS pathophysiology. We also compare ALS to other motor neuron diseases and draw perspectives for future research and treatment.

Muscle Involvement in Amyotrophic Lateral Sclerosis: Understanding the Pathogenesis and Advancing Therapeutics

Amyotrophic lateral sclerosis (ALS) is a fatal condition characterized by the selective loss of motor neurons in the motor cortex, brainstem, and spinal cord. Muscle involvement, muscle atrophy, and subsequent paralysis are among the main features of this disease, which is defined as a neuromuscular disorder. ALS is a persistently progressive disease, and as motor neurons continue to degenerate, individuals with ALS experience a gradual decline in their ability to perform daily activities. Ultimately, muscle function loss may result in paralysis, presenting significant challenges in mobility, communication, and self-care. While the majority of ALS research has traditionally focused on pathogenic pathways in the central nervous system, there has been a great interest in muscle research. These studies were carried out on patients and animal models in order to better understand the molecular mechanisms involved and to develop therapies aimed at improving muscle function. This review summarizes the features of ALS and discusses the role of muscle, as well as examines recent studies in the development of treatments.

Interplay between Protein Kinase C Epsilon and Reactive Oxygen Species during Myogenic Differentiation

Reactive oxygen species (ROS) are currently recognized as a key driver of several physiological processes. Increasing evidence indicates that ROS levels can affect myogenic differentiation, but the molecular mechanisms still need to be elucidated. Protein kinase C (PKC) epsilon (PKCe) promotes muscle stem cell differentiation and regeneration of skeletal muscle after injury. PKCs play a tissue-specific role in redox biology, with specific isoforms being both a target of ROS and an up-stream regulator of ROS production. Therefore, we hypothesized that PKCe represents a molecular link between redox homeostasis and myogenic differentiation. We used an in vitro model of a mouse myoblast cell line (C2C12) to study the PKC-redox axis. We demonstrated that the transition from a myoblast to myotube is typified by increased PKCe protein content and decreased ROS. Intriguingly, the expression of the antioxidant enzyme superoxide dismutase 2 (SOD2) is significantly higher in the late phases of myogenic differentiation, mimicking PKCe protein content. Furthermore, we demonstrated that PKCe inhibition increases ROS and reduces SOD2 protein content while SOD2 silencing did not affect PKCe protein content, suggesting that the kinase could be an up-stream regulator of SOD2. To support this hypothesis, we found that in C2C12 cells, PKCe interacts with Nrf2, whose activation induces SOD2 transcription. Overall, our results indicate that PKCe is capable of activating the antioxidant signaling preventing ROS accumulation in a myotube, eventually promoting myogenic differentiation.

Recent Advances in Extracellular Vesicles in Amyotrophic Lateral Sclerosis and Emergent Perspectives

Amyotrophic lateral sclerosis (ALS) is a severe and incurable neurodegenerative disease characterized by the progressive death of motor neurons, leading to paralysis and death. It is a rare disease characterized by high patient-to-patient heterogeneity, which makes its study arduous and complex. Extracellular vesicles (EVs) have emerged as important players in the development of ALS. Thus, ALS phenotype-expressing cells can spread their abnormal bioactive cargo through the secretion of EVs, even in distant tissues. Importantly, owing to their nature and composition, EVs' formation and cargo can be exploited for better comprehension of this elusive disease and identification of novel biomarkers, as well as for potential therapeutic applications, such as those based on stem cell-derived exosomes. This review highlights recent advances in the identification of the role of EVs in ALS etiopathology and how EVs can be promising new therapeutic strategies.

Sympathetic neuropathology is revealed in muscles affected by amyotrophic lateral sclerosis

Rationale: The anatomical substrate of skeletal muscle autonomic innervation has remained underappreciated since it was described many decades ago. As such, the structural and functional features of muscle sympathetic innervation are largely undetermined in both physiology and pathology, mainly due to methodological limitations in the histopathological analysis of small neuronal fibers in tissue samples. Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disease which mainly targets motor neurons, and despite autonomic symptoms occurring in a significant fraction of patients, peripheral sympathetic neurons (SNs) are generally considered unaffected and, as such, poorly studied. Purpose: In this research, we compared sympathetic innervation of normal and ALS muscles, through structural analysis of the sympathetic network in human and murine tissue samples. Methods and Results: We first refined tissue processing to circumvent methodological limitations interfering with the detection of muscle sympathetic innervation. The optimized "Neuro Detection Protocol" (NDP) was validated in human muscle biopsies, demonstrating that SNs innervate, at high density, both blood vessels and skeletal myofibers, independent of the fiber metabolic type. Subsequently, NDP was exploited to analyze sympathetic innervation in muscles of SOD1^G93A mice, a preclinical ALS model. Our data show that ALS murine muscles display SN denervation, which has already initiated at the early disease stage and worsened during aging. SN degeneration was also observed in muscles of MLC/SOD1^G93A mice, with muscle specific expression of the SOD1^G93A mutant gene. Notably, similar alterations in SNs were observed in muscle biopsies from an ALS patient, carrying the SOD1^G93A mutation. Conclusion: We set up a protocol for the analysis of murine and, more importantly, human muscle sympathetic innervation. Our results indicate that SNs are additional cell types compromised in ALS and suggest that dysfunctional SOD1^G93A muscles affect their sympathetic innervation.

Functional Nutrients to Ameliorate Neurogenic Muscle Atrophy

Neurogenic muscle atrophy is a debilitating condition that occurs from nerve trauma in association with diseases or during aging, leading to reduced interaction between motoneurons and skeletal fibers. Current therapeutic approaches aiming at preserving muscle mass in a scenario of decreased nervous input include physical activity and employment of drugs that slow down the progression of the condition yet provide no concrete resolution. Nutritional support appears as a precious tool, adding to the success of personalized medicine, and could thus play a relevant part in mitigating neurogenic muscle atrophy. We herein summarize the molecular pathways triggered by denervation of the skeletal muscle that could be affected by functional nutrients. In this narrative review, we examine and discuss studies pertaining to the use of functional ingredients to counteract neurogenic muscle atrophy, focusing on their preventive or curative means of action within the skeletal muscle. We reviewed experimental models of denervation in rodents and in amyotrophic lateral sclerosis, as well as that caused by aging, considering the knowledge generated with use of animal experimental models and, also, from human studies.

Muscle cells of sporadic amyotrophic lateral sclerosis patients secrete neurotoxic vesicles

BACKGROUND

The cause of the motor neuron (MN) death that drives terminal pathology in amyotrophic lateral sclerosis (ALS) remains unknown, and it is thought that the cellular environment of the MN may play a key role in MN survival. Several lines of evidence implicate vesicles in ALS, including that extracellular vesicles may carry toxic elements from astrocytes towards MNs, and that pathological proteins have been identified in circulating extracellular vesicles of sporadic ALS patients. Because MN degeneration at the neuromuscular junction is a feature of ALS, and muscle is a vesicle-secretory tissue, we hypothesized that muscle vesicles may be involved in ALS pathology.

METHODS

Sporadic ALS patients were confirmed to be ALS according to El Escorial criteria and were genotyped to test for classic gene mutations associated with ALS, and physical function was assessed using the ALSFRS-R score. Muscle biopsies of either mildly affected deltoids of ALS patients (n = 27) or deltoids of aged-matched healthy subjects (n = 30) were used for extraction of muscle stem cells, to perform immunohistology, or for electron microscopy. Muscle stem cells were characterized by immunostaining, RT-qPCR, and transcriptomic analysis. Secreted muscle vesicles were characterized by proteomic analysis, Western blot, NanoSight, and electron microscopy. The effects of muscle vesicles isolated from the culture medium of ALS and healthy myotubes were tested on healthy human-derived iPSC MNs and on healthy human myotubes, with untreated cells used as controls.

RESULTS

An accumulation of multivesicular bodies was observed in muscle biopsies of sporadic ALS patients by immunostaining and electron microscopy. Study of muscle biopsies and biopsy-derived denervation-naïve differentiated muscle stem cells (myotubes) revealed a consistent disease signature in ALS myotubes, including intracellular accumulation of exosome-like vesicles and disruption of RNA-processing. Compared with vesicles from healthy control myotubes, when administered to healthy MNs the vesicles of ALS myotubes induced shortened, less branched neurites, cell death, and disrupted localization of RNA and RNA-processing proteins. The RNA-processing protein FUS and a majority of its binding partners were present in ALS muscle vesicles, and toxicity was dependent on the expression level of FUS in recipient cells. Toxicity to recipient MNs was abolished by anti-CD63 immuno-blocking of vesicle uptake.

CONCLUSIONS

ALS muscle vesicles are shown to be toxic to MNs, which establishes the skeletal muscle as a potential source of vesicle-mediated toxicity in ALS.

Therapeutic Targets in Amyotrophic Lateral Sclerosis: Focus on Ion Channels and Skeletal Muscle

Amyotrophic Lateral Sclerosis is a neurodegenerative disease caused by progressive loss of motor neurons, which severely compromises skeletal muscle function. Evidence shows that muscle may act as a molecular powerhouse, whose final signals generate in patients a progressive loss of voluntary muscle function and weakness leading to paralysis. This pathology is the result of a complex cascade of events that involves a crosstalk among motor neurons, glia, and muscles, and evolves through the action of converging toxic mechanisms. In fact, mitochondrial dysfunction, which leads to oxidative stress, is one of the mechanisms causing cell death. It is a common denominator for the two existing forms of the disease: sporadic and familial. Other factors include excitotoxicity, inflammation, and protein aggregation. Currently, there are limited cures. The only approved drug for therapy is riluzole, that modestly prolongs survival, with edaravone now waiting for new clinical trial aimed to clarify its efficacy. Thus, there is a need of effective treatments to reverse the damage in this devastating pathology. Many drugs have been already tested in clinical trials and are currently under investigation. This review summarizes the already tested drugs aimed at restoring muscle-nerve cross-talk and on new treatment options targeting this tissue.

From the Bench to the Bedside: Branched Amino Acid and Micronutrient Strategies to Improve Mitochondrial Dysfunction Leading to Sarcopenia

With extended life expectancy, the older population is constantly increasing, and consequently, so too is the prevalence of age-related disorders. Sarcopenia, the pathological age-related loss of muscle mass and function; and malnutrition, the imbalance in nutrient intake and resultant energy production, are both commonly occurring conditions in old adults. Altered nutrition plays a crucial role in the onset of sarcopenia, and both these disorders are associated with detrimental consequences for patients (e.g., frailty, morbidity, and mortality) and society (e.g., healthcare costs). Importantly, sarcopenia and malnutrition also share critical molecular alterations, such as mitochondrial dysfunction, increased oxidative stress, and a chronic state of low grade and sterile inflammation, defined as inflammageing. Given the connection between malnutrition and sarcopenia, nutritional interventions capable of affecting mitochondrial health and correcting inflammageing are emerging as possible strategies to target sarcopenia. Here, we discuss mitochondrial dysfunction, oxidative stress, and inflammageing as key features leading to sarcopenia. Moreover, we examine the effects of some branched amino acids, omega-3 PUFA, and selected micronutrients on these pathways, and their potential role in modulating sarcopenia, warranting further clinical investigation.

Neuromuscular Junction Dysfunction in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by progressive degeneration of motor neurons leading to skeletal muscle denervation. Earlier studies have shown that motor neuron degeneration begins in motor cortex and descends to the neuromuscular junction (NMJ) in a dying forward fashion. However, accumulating evidences support that ALS is a distal axonopathy where early pathological changes occur at the NMJ, prior to onset of clinical symptoms and propagates towards the motor neuron cell body supporting "dying back" hypothesis. Despite several evidences, series of events triggering NMJ disassembly in ALS are still obscure. Neuromuscular junction is a specialized tripartite chemical synapse which involves a well-coordinated communication among the presynaptic motor neuron, postsynaptic skeletal muscle, and terminal Schwann cells. This review provides comprehensive insight into the role of NMJ in ALS pathogenesis. We have emphasized the molecular alterations in cellular components of NMJ leading to loss of effective neuromuscular transmission in ALS. Further, we provide a preview into research involved in exploring NMJ as potential target for designing effective therapies for ALS.

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.

4,4'-Dimethoxychalcone regulates redox homeostasis by targeting riboflavin metabolism in Parkinson's disease therapy

Oxidative stress damage plays a pivotal role in Parkinson's disease (PD) pathogenesis. Previously, we developed a blood brain barrier-penetrating peptide-based "Trojan Horse" strategy to deliver 4,4'-dimethoxychalcone (DMC) for PD therapy and revealed neuroprotective properties of DMC in a PD model; however, the underlying mechanisms remained unclear. Here, we report that DMC attenuated motor impairment, degeneration of DA neurons and α-synuclein aggregation in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and exogenous human α-synuclein-induced PD mouse models. Mechanistically, DMC increased the expression of two critical intermediates in riboflavin metabolism: riboflavin kinase (RFK) and its metabolic product, flavin mononucleotide (FMN). We provide the first direct evidence that FMN ameliorated oxidative stress damage and dopaminergic neuron degeneration both in vitro and in vivo and that riboflavin metabolism was required for DMC-mediated neuroprotection. DMC-induced restoration of redox homeostasis was mediated via the activation of protein kinase Cθ (PKCθ) signaling. Together, our findings reveal that DMC may serve as a novel antioxidant in PD intervention and also define a novel mechanism that underlies its therapeutic activity.

Alterations in fast-twitch muscle membrane conductance regulation do not explain decreased muscle function of SOD1G93A rats

INTRODUCTION/AIMS

Both neuromuscular junction (NMJ) dysfunction and altered electrophysiological properties of muscle fibers have been reported in amyotrophic lateral sclerosis (ALS) patients. ALS-related preclinical studies typically use rodent SOD1^G93A overexpression models, but translation to the human disease has been challenged. The present work explored NMJ function and cellular electrophysiological properties of muscles fibers in SOD1^G93A overexpression rats.

METHODS

Longitudinal studies of compound muscle action potentials (CMAPs) were performed in SOD1^G93A rats. Cellular studies were performed to evaluate electrophysiological properties of muscle fibers, including the resting membrane conductance (G_m ) and its regulation during prolonged action potential (AP) firing.

RESULTS

SOD1^G93A rats showed a substantial loss of gastrocnemius CMAP amplitude (35.8 mV, P < .001) and a minor increase in CMAP decrement (8.5%, P = .002) at 25 weeks. In addition, SOD1^G93A EDL muscle fibers showed a lower baseline G_m (wild-type, 1325 μS/cm² ; SOD1^G93A , 1137 μS/cm² ; P < .001) and minor alterations in G_m regulation during repeated firing of APs as compared with wild-type rats.

DISCUSSION

The current data suggest that loss of CMAP amplitude is largely explained by defects in either lower motor neuron or skeletal muscle with only minor indications of a role for neuromuscular transmission defects in SOD1^G93A rats. Electrophysiological properties of muscle fibers were not markedly affected, and an elevated G_m , as has been reported in motor neuron disease (MND) patients, was not replicated in SOD1^G93A muscles. Collectively, the neuromuscular pathology of SOD1^G93A rats appears to differ from that of ALS/MND patients with respect to neuromuscular transmission defects and electrophysiological properties of muscle fibers.

Lithium causes differential effects on postsynaptic stability in normal and denervated neuromuscular synapses

Lithium chloride has been widely used as a therapeutic mood stabilizer. Although cumulative evidence suggests that lithium plays modulatory effects on postsynaptic receptors, the underlying mechanism by which lithium regulates synaptic transmission has not been fully elucidated. In this work, by using the advantageous neuromuscular synapse, we evaluated the effect of lithium on the stability of postsynaptic nicotinic acetylcholine receptors (nAChRs) in vivo. We found that in normally innervated neuromuscular synapses, lithium chloride significantly decreased the turnover of nAChRs by reducing their internalization. A similar response was observed in CHO-K1/A5 cells expressing the adult muscle-type nAChRs. Strikingly, in denervated neuromuscular synapses, lithium led to enhanced nAChR turnover and density by increasing the incorporation of new nAChRs. Lithium also potentiated the formation of unstable nAChR clusters in non-synaptic regions of denervated muscle fibres. We found that denervation-dependent re-expression of the foetal nAChR γ-subunit was not altered by lithium. However, while denervation inhibits the distribution of β-catenin within endplates, lithium-treated fibres retain β-catenin staining in specific foci of the synaptic region. Collectively, our data reveal that lithium treatment differentially affects the stability of postsynaptic receptors in normal and denervated neuromuscular synapses in vivo, thus providing novel insights into the regulatory effects of lithium on synaptic organization and extending its potential therapeutic use in conditions affecting the peripheral nervous system.

Redox Signaling and Sarcopenia: Searching for the Primary Suspect

Sarcopenia, the age-related decline in muscle mass and function, derives from multiple etiological mechanisms. Accumulative research suggests that reactive oxygen species (ROS) generation plays a critical role in the development of this pathophysiological disorder. In this communication, we review the various signaling pathways that control muscle metabolic and functional integrity such as protein turnover, cell death and regeneration, inflammation, organismic damage, and metabolic functions. Although no single pathway can be identified as the most crucial factor that causes sarcopenia, age-associated dysregulation of redox signaling appears to underlie many deteriorations at physiological, subcellular, and molecular levels. Furthermore, discord of mitochondrial homeostasis with aging affects most observed problems and requires our attention. The search for the primary suspect of the fundamental mechanism for sarcopenia will likely take more intense research for the secret of this health hazard to the elderly to be unlocked.

The Skeletal Muscle Emerges as a New Disease Target in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that leads to progressive degeneration of motor neurons (MNs) and severe muscle atrophy without effective treatment. Most research on ALS has been focused on the study of MNs and supporting cells of the central nervous system. Strikingly, the recent observations of pathological changes in muscle occurring before disease onset and independent from MN degeneration have bolstered the interest for the study of muscle tissue as a potential target for delivery of therapies for ALS. Skeletal muscle has just been described as a tissue with an important secretory function that is toxic to MNs in the context of ALS. Moreover, a fine-tuning balance between biosynthetic and atrophic pathways is necessary to induce myogenesis for muscle tissue repair. Compromising this response due to primary metabolic abnormalities in the muscle could trigger defective muscle regeneration and neuromuscular junction restoration, with deleterious consequences for MNs and thereby hastening the development of ALS. However, it remains puzzling how backward signaling from the muscle could impinge on MN death. This review provides a comprehensive analysis on the current state-of-the-art of the role of the skeletal muscle in ALS, highlighting its contribution to the neurodegeneration in ALS through backward-signaling processes as a newly uncovered mechanism for a peripheral etiopathogenesis of the disease.

Age-Related Alterations at Neuromuscular Junction: Role of Oxidative Stress and Epigenetic Modifications

With advancing aging, a decline in physical abilities occurs, leading to reduced mobility and loss of independence. Although many factors contribute to the physio-pathological effects of aging, an important event seems to be related to the compromised integrity of the neuromuscular system, which connects the brain and skeletal muscles via motoneurons and the neuromuscular junctions (NMJs). NMJs undergo severe functional, morphological, and molecular alterations during aging and ultimately degenerate. The effect of this decline is an inexorable decrease in skeletal muscle mass and strength, a condition generally known as sarcopenia. Moreover, several studies have highlighted how the age-related alteration of reactive oxygen species (ROS) homeostasis can contribute to changes in the neuromuscular junction morphology and stability, leading to the reduction in fiber number and innervation. Increasing evidence supports the involvement of epigenetic modifications in age-dependent alterations of the NMJ. In particular, DNA methylation, histone modifications, and miRNA-dependent gene expression represent the major epigenetic mechanisms that play a crucial role in NMJ remodeling. It is established that environmental and lifestyle factors, such as physical exercise and nutrition that are susceptible to change during aging, can modulate epigenetic phenomena and attenuate the age-related NMJs changes. This review aims to highlight the recent epigenetic findings related to the NMJ dysregulation during aging and the role of physical activity and nutrition as possible interventions to attenuate or delay the age-related decline in the neuromuscular system.

Mini-Review: Induced pluripotent stem cells and the search for new cell-specific ALS therapeutic targets

Amongst the most important discoveries in ALS pathobiology are the works demonstrating that multiple cell types contribute to disease onset and progression. However, a significant limitation in ALS research is the inability to obtain tissues from ALS patient brain and spinal cord during the course of the disease. In vivo modeling has provided insights into the role of these cell subtypes in disease onset and progression. However, in vivo models also have shortcomings, including the reliance on a limited number of models based upon hereditary forms of the disease. Therefore, using human induced pluripotent stem cells (iPSC) reprogrammed from somatic cells of ALS patients, with both hereditary and sporadic forms of the disease, and differentiated into cell subtypes of both the central nervous system (CNS) and peripheral nervous system (PNS), have become powerful complementary tools for investigating basic mechanisms of disease as well as a platform for drug discovery. Motor neuron and other neuron subtypes, as well as non-neuronal cells have been differentiated from human iPSC and studied for their potential contributions to ALS pathobiology. As iPSC technologies have advanced, 3D modeling with multicellular systems organised in microfluidic chambers or organoids are the next step in validating the pathways and therapeutic targets already identified. Precision medicine approaches with iPSC using either traditional strategies of screening drugs that target a known pathogenic mechanism as well as "blind-to-target" drug screenings that allow for patient stratification based on drug response rather than clinical characteristics are now being employed.

Signal Transduction in Immune Cells and Protein Kinases

Immune response relies upon several intracellular signaling events. Among the protein kinases involved in these pathways, members of the protein kinase C (PKC) family are prominent molecules because they have the capacity to acutely and reversibly modulate effector protein functions, controlling both spatial distribution and dynamic properties of the signals. Different PKC isoforms are involved in distinct signaling pathways, with selective functions in a cell-specific manner.In innate system, Toll-like receptor signaling is the main molecular event triggering effector functions. Various isoforms of PKC can be common to different TLRs, while some of them are specific for a certain type of TLR. Protein kinases involvement in innate immune cells are presented within the chapter emphasizing their coordination in many aspects of immune cell function and, as important players in immune regulation.In adaptive immunity T-cell receptor and B-cell receptor signaling are the main intracellular pathways involved in seminal immune specific cellular events. Activation through TCR and BCR can have common intracellular pathways while others can be specific for the type of receptor involved or for the specific function triggered. Various PKC isoforms involvement in TCR and BCR Intracellular signaling will be presented as positive and negative regulators of the immune response events triggered in adaptive immunity.

Skeletal Muscle-Restricted Expression of Human SOD1 in Transgenic Mice Causes a Fatal ALS-Like Syndrome

Amyotrophic lateral sclerosis (ALS) is a fatal heterogeneous neurodegenerative disease that causes motor neuron (MN) loss and skeletal muscle paralysis. It is uncertain whether this degeneration of MNs is triggered intrinsically and is autonomous, or if the disease initiating mechanisms are extrinsic to MNs. We hypothesized that skeletal muscle is a primary site of pathogenesis in ALS that triggers MN degeneration. Some inherited forms of ALS are caused by mutations in the superoxide dismutase-1 (SOD1) gene, that encodes an antioxidant protein, so we created transgenic (tg) mice expressing wild-type-, G37R-, and G93A-human SOD1 gene variants only in skeletal muscle. Presence of human SOD1 (hSOD1) protein in skeletal muscle was verified by western blotting, enzyme activity gels, and immunofluorescence in myofibers and satellite cells. These tg mice developed limb weakness and paresis with motor deficits, limb and chest muscle wasting, diaphragm atrophy, and age-related fatal disease with a lifespan shortening of 10–16%. Brown and white adipose tissue also became wasted. Myofibers of tg mice developed crystalline-like inclusions, individualized sarcomere destruction, mitochondriopathy with vesiculation, DNA damage, and activated p53. Satellite cells became apoptotic. The diaphragm developed severe loss of neuromuscular junction presynaptic and postsynaptic integrity, including decreased innervation, loss of synaptophysin, nitration of synaptophysin, and loss of nicotinic acetylcholine receptor and scaffold protein rapsyn. Co-immunoprecipitation identified hSOD1 interaction with rapsyn. Spinal cords of tg mice developed gross atrophy. Spinal MNs formed cytoplasmic and nuclear inclusions, axonopathy, mitochondriopathy, accumulated DNA damage, activated p53 and cleaved caspase-3, and died. Tg mice had a 40–50% loss of MNs. This work shows that hSOD1 in skeletal muscle is a driver of pathogenesis in ALS, that involves myofiber and satellite cell toxicity, and apparent muscle-adipose tissue disease relationships. It also identifies a non-autonomous mechanism for MN degeneration explaining their selective vulnerability as likely a form of target-deprivation retrograde neurodegeneration.

Impairment Mechanisms and Intervention Approaches for Aged Human Neuromuscular Junctions

The neuromuscular junction (NMJ) is a chemical synapse formed between a presynaptic motor neuron and a postsynaptic muscle cell. NMJs in most vertebrate species share many essential features; however, some differences distinguish human NMJs from others. This review will describe the pre- and postsynaptic structures of human NMJs and compare them to NMJs of laboratory animals. We will focus on age-dependent declines in function and changes in the structure of human NMJs. Furthermore, we will describe insights into the aging process revealed from mouse models of accelerated aging. In addition, we will compare aging phenotypes to other human pathologies that cause impairments of pre- and postsynaptic structures at NMJs. Finally, we will discuss potential intervention approaches for attenuating age-related NMJ dysfunction and sarcopenia in humans.

Protein kinase inhibitors for amyotrophic lateral sclerosis therapy

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder that causes the progressive loss of motoneurons and, unfortunately, there is no effective treatment for this disease. Interconnecting multiple pathological mechanisms are involved in the neuropathology of this disease, including abnormal aggregation of proteins, neuroinflammation and dysregulation of the ubiquitin proteasome system. Such complex mechanisms, together with the lack of reliable animal models of the disease have hampered the development of drugs for this disease. Protein kinases, a key pharmacological target in several diseases, have been linked to ALS as they play a central role in the pathology of many diseases. Therefore several inhibitors are being currently trailed for clinical proof of concept in ALS patients. In this review, we examine the recent literature on protein kinase inhibitors currently in pharmaceutical development for this diseaseas future therapy for AS together with their involvement in the pathobiology of ALS. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

The TOR Pathway at the Neuromuscular Junction: More Than a Metabolic Player?

The neuromuscular junction (NMJ) is the chemical synapse connecting motor neurons and skeletal muscle fibers. NMJs allow all voluntary movements, and ensure vital functions like breathing. Changes in the structure and function of NMJs are hallmarks of numerous pathological conditions that affect muscle function including sarcopenia, the age-related loss of muscle mass and function. However, the molecular mechanisms leading to the morphological and functional perturbations in the pre- and post-synaptic compartments of the NMJ remain poorly understood. Here, we discuss the role of the metabolic pathway associated to the kinase TOR (Target of Rapamycin) in the development, maintenance and alterations of the NMJ. This is of particular interest as the TOR pathway has been implicated in aging, but its role at the NMJ is still ill-defined. We highlight the respective functions of the two TOR-associated complexes, TORC1 and TORC2, and discuss the role of localized protein synthesis and autophagy regulation in motor neuron terminals and sub-synaptic regions of muscle fibers and their possible effects on NMJ maintenance.

Changes in Expression and Cellular Localization of Rat Skeletal Muscle ClC-1 Chloride Channel in Relation to Age, Myofiber Phenotype and PKC Modulation

The ClC-1 chloride channel 1 is important for muscle function as it stabilizes resting membrane potential and helps to repolarize the membrane after action potentials. We investigated the contribution of ClC-1 to adaptation of skeletal muscles to needs induced by the different stages of life. We analyzed the ClC-1 gene and protein expression as well as mRNA levels of protein kinase C (PKC) alpha and theta involved in ClC-1 modulation, in soleus (SOL) and extensor digitorum longus (EDL) muscles of rats in all stage of life. The cellular localization of ClC-1 in relation to age was also investigated. Our data show that during muscle development ClC-1 expression differs according to phenotype. In fast-twitch EDL muscles ClC-1 expression increased 10-fold starting at 7 days up to 8 months of life. Conversely, in slow-twitch SOL muscles ClC-1 expression remained constant until 33 days of life and subsequently increased fivefold to reach the adult value. Aging induced a downregulation of gene and protein ClC-1 expression in both muscle types analyzed. The mRNA of PKC-theta revealed the same trend as ClC-1 except in old age, whereas the mRNA of PKC-alpha increased only after 2 months of age. Also, we found that the ClC-1 is localized in both membrane and cytoplasm, in fibers of 12-day-old rats, becoming perfectly localized on the membrane in 2-month-old rats. This study could represent a point of comparison helpful for the identification of accurate pharmacological strategies for all the pathological situations in which ClC-1 protein is altered.

Decoding the relationship between ageing and amyotrophic lateral sclerosis: a cellular perspective

With an ageing population comes an inevitable increase in the prevalence of age-associated neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS), a relentlessly progressive and universally fatal disease characterized by the degeneration of upper and lower motor neurons within the brain and spinal cord. Indeed, the physiological process of ageing causes a variety of molecular and cellular phenotypes. With dysfunction at the neuromuscular junction implicated as a key pathological mechanism in ALS, and each lower motor unit cell type vulnerable to its own set of age-related phenotypes, the effects of ageing might in fact prove a prerequisite to ALS, rendering the cells susceptible to disease-specific mechanisms. Moreover, we discuss evidence for overlap between age and ALS-associated hallmarks, potentially implicating cell type-specific ageing as a key contributor to this multifactorial and complex disease. With a dearth of disease-modifying therapy currently available for ALS patients and a substantial failure in bench to bedside translation of other potential therapies, the unification of research in ageing and ALS requires high fidelity models to better recapitulate age-related human disease and will ultimately yield more reliable candidate therapeutics for patients, with the aim of enhancing healthspan and life expectancy.

Antitumorigenic Effects of Inhibiting Ephrin Receptor Kinase Signaling by GLPG1790 against Colorectal Cancer Cell Lines In Vitro and In Vivo

Erythropoietin-producing hepatocellular receptors (Eph) promote the onset and sustain the progression of cancers such as colorectal cancer (CRC), in which the A2 subtype of Eph receptor expression has been shown to correlate with a poor prognosis and has been identified as a promising therapeutic target. Herein, we investigated, in vitro and in vivo, the effects of treatment with GLPG1790, a potent pan-Eph inhibitor. The small molecule has selective activity against the EphA2 isoform in human HCT116 and HCT15 CRC cell lines expressing a constitutively active form of RAS concurrently with a wild-type or mutant form of p53, respectively. GLPG1790 reduced EPHA2 phosphorylation/activation and induced G₁/S cell-cycle growth arrest by downregulating the expression of cyclin E and PCNA, while upregulating p21^Waf1/Cip1 and p27^Cip/Kip. The inhibition of ephrin signaling induced quiescence in HCT15 and senescence in HCT116 cells. While investigating the role of CRC-related, pro-oncogenic p53 and RAS pathways, we found that GLPG1790 upregulated p53 expression and that silencing p53 or inhibiting RAS (human rat sarcoma)/ERKs (extracellular signal-regulated kinase) signaling restrained the ability of GLPG1790 to induce senescence in HCT116 cells. On the other hand, HCT15 silencing of p53 predisposed cells to GLPG1790-induced senescence, whilst no effects of ERK inhibition were observed. Finally, GLPG1790 hindered the epithelial-mesenchymal transition, reduced the migratory capacities of CRC, and affected tumor formation in xenograft models in vivo more efficiently using HCT116 than HCT15 for xenografts. Taken together, our data suggest the therapeutic potential of GLPG1790 as a signal transduction-based therapeutic strategy in to treat CRC.

Oligodendrocytes Death Induced Sensorimotor and Cognitive Deficit in N-nitro-L-arginine methyl Rat Model of Pre-eclampsia

Pre-eclampsia (PE) is a pregnancy complicated syndrome that affects multiple organs including the brain that continue post- delivery in both mother and the offspring. We evaluated the expression of oligodendrocytes in the brain of PE rat model through development as well as the cognitive changes and other behavioural modifications that may occur later in the life of offspring of PE-like rat model. Pregnant rats divided into early-onset and late-onset groups were administered with N-nitro- L-arginine methyl (L-NAME) through drinking water at gestational days (GD) 8-17. Rats were allowed free access to water throughout the pregnancy. At GD 19, post-natal day (PND) 1 and 60, rats were sacrificed and brain excised for further analysis. The offspring were subjected to behavioural studies for cognitive and sensorimotor impairments before sacrificed at PND 60. Results showed significant down-regulation in the expression of OLIG2 in PE at GD 19 brain which persists till PND 60. Likewise, there was a significant increase in the latency to locate the platform in Morris water maze, time to traverse the balance beam and reduced hanging time on the wire test between the control and the PE treated. PE could lead to impaired neuronal signalling through demyelination which may contributes significantly to long-term sensorimotor and cognitive deficit.

The Impact of Kinases in Amyotrophic Lateral Sclerosis at the Neuromuscular Synapse: Insights into BDNF/TrkB and PKC Signaling

Brain-derived neurotrophic factor (BDNF) promotes neuron survival in adulthood in the central nervous system. In the peripheral nervous system, BDNF is a contraction-inducible protein that, through its binding to tropomyosin-related kinase B receptor (TrkB), contributes to the retrograde neuroprotective control done by muscles, which is necessary for motor neuron function. BDNF/TrkB triggers downstream presynaptic pathways, involving protein kinase C, essential for synaptic function and maintenance. Undeniably, this reciprocally regulated system exemplifies the tight communication between nerve terminals and myocytes to promote synaptic function and reveals a new view about the complementary and essential role of pre and postsynaptic interplay in keeping the synapse healthy and strong. This signaling at the neuromuscular junction (NMJ) could establish new intervention targets across neuromuscular diseases characterized by deficits in presynaptic activity and muscle contractility and by the interruption of the connection between nervous and muscular tissues, such as amyotrophic lateral sclerosis (ALS). Indeed, exercise and other therapies that modulate kinases are effective at delaying ALS progression, preserving NMJs and maintaining motor function to increase the life quality of patients. Altogether, we review synaptic activity modulation of the BDNF/TrkB/PKC signaling to sustain NMJ function, its and other kinases’ disturbances in ALS and physical and molecular mechanisms to delay disease progression.

Increased Circulating Levels of Interleukin-6 Affect the Redox Balance in Skeletal Muscle

The extent of oxidative stress and chronic inflammation are closely related events which coexist in a muscle environment under pathologic conditions. It has been generally accepted that the inflammatory cells, as well as myofibers, are sources of reactive species which are, in turn, able to amplify the activation of proinflammatory pathways. However, the precise mechanism underlining the physiopathologic interplay between ROS generation and inflammatory response has to be fully clarified. Thus, the identification of key molecular players in the interconnected pathogenic network between the two processes might help to design more specific therapeutic approaches for degenerative diseases. Here, we investigated whether elevated circulating levels of the proinflammatory cytokine Interleukin-6 (IL-6) are sufficient to perturb the physiologic redox balance in skeletal muscle, independently of tissue damage and inflammatory response. We observed that the overexpression of circulating IL-6 enhances the generation and accumulation of free radicals in the diaphragm muscle of adult NSE/IL-6 mice, by deregulating redox-associated molecular circuits and impinging the nuclear factor erythroid 2-related factor 2- (Nrf2-) mediated antioxidant response. Our findings are coherent with a model in which uncontrolled levels of IL-6 in the bloodstream can influence the local redox homeostasis, inducing the establishment of prooxidative conditions in skeletal muscle tissue.

Neuromuscular Junction as an Entity of Nerve-Muscle Communication

One of the crucial systems severely affected in several neuromuscular diseases is the loss of effective connection between muscle and nerve, leading to a pathological non-communication between the two tissues. The neuromuscular junction (NMJ) represents the critical region at the level of which muscle and nerve communicate. Defects in signal transmission between terminal nerve endings and muscle membrane is a common feature of several physio-pathologic conditions including aging and Amyotrophic Lateral Sclerosis (ALS). Nevertheless, controversy exists on whether pathological events beginning at the NMJ precede or follow loss of motor units. In this review, the role of NMJ in the physio-pathologic interplay between muscle and nerve is discussed.

β-catenin aggregation in models of ALS motor neurons: GSK3β inhibition effect and neuronal differentiation

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by motor neuron death. A 20% of familial ALS cases are associated with mutations in the gene coding for superoxide dismutase 1 (SOD1). The accumulation of abnormal aggregates of different proteins is a common feature in motor neurons of patients and transgenic ALS mice models, which are thought to contribute to disease pathogenesis. Developmental morphogens, such as the Wnt family, regulate numerous features of neuronal physiology in the adult brain and have been implicated in neurodegeneration. β-catenin is a central mediator of both, Wnt signaling activity and cell-cell interactions. We previously reported that the expression of mutant SOD1 in the NSC34 motor neuron cell line decreases basal Wnt pathway activity, which correlates with cytosolic β-catenin accumulation and impaired neuronal differentiation. In this work, we aimed a deeper characterization of β-catenin distribution in models of ALS motor neurons. We observed extensive accumulation of β-catenin supramolecular structures in motor neuron somas of pre-symptomatic mutant SOD1 mice. In cell-cell appositional zones of NSC34 cells expressing mutant SOD1, β-catenin displays a reduced co-distribution with E-cadherin accompanied by an increased association with the gap junction protein Connexin-43; these findings correlate with impaired intercellular adhesion and exacerbated cell coupling. Remarkably, pharmacological inhibition of the glycogen synthase kinase-3β (GSK3β) in both NSC34 cell lines reverted both, β-catenin aggregation and the adverse effects of mutant SOD1 expression on neuronal differentiation. Our findings suggest that early defects in β-catenin distribution could be an underlying factor affecting the onset of neurodegeneration in familial ALS.

Motor Endplate-Anatomical, Functional, and Molecular Concepts in the Historical Perspective

By mediating voluntary muscle movement, vertebrate neuromuscular junctions (NMJ) play an extraordinarily important role in physiology. While the significance of the nerve-muscle connectivity was already conceived almost 2000 years back, the precise cell and molecular biology of the NMJ have been revealed in a series of fascinating research activities that started around 180 years ago and that continues. In all this time, NMJ research has led to fundamentally new concepts of cell biology, and has triggered groundbreaking advancements in technologies. This review tries to sketch major lines of thought and concepts on NMJ in their historical perspective, in particular with respect to anatomy, function, and molecular components. Furthermore, along these lines, it emphasizes the mutual benefit between science and technology, where one drives the other. Finally, we speculate on potential major future directions for studies on NMJ in these fields.

Atrophy, oxidative switching and ultrastructural defects in skeletal muscle of the ataxia telangiectasia mouse model

Ataxia telangiectasia is a rare, multi system disease caused by ATM kinase deficiency. Atm-knockout mice recapitulate premature aging, immunodeficiency, cancer predisposition, growth retardation and motor defects, but not cerebellar neurodegeneration and ataxia. We explored whether Atm loss is responsible for skeletal muscle defects by investigating myofiber morphology, oxidative/glycolytic activity, myocyte ultrastructural architecture and neuromuscular junctions. Atm-knockout mice showed reduced muscle and fiber size. Atrophy, protein synthesis impairment and a switch from glycolytic to oxidative fibers were detected, along with an increase of in expression of slow and fast myosin types (Myh7, and Myh2 and Myh4, respectively) in tibialis anterior and solei muscles isolated from Atm-knockout mice. Transmission electron microscopy of tibialis anterior revealed misalignments of Z-lines and sarcomeres and mitochondria abnormalities that were associated with an increase in reactive oxygen species. Moreover, neuromuscular junctions appeared larger and more complex than those in Atm wild-type mice, but with preserved presynaptic terminals. In conclusion, we report for the first time that Atm-knockout mice have clear morphological skeletal muscle defects that will be relevant for the investigation of the oxidative stress response, motor alteration and the interplay with peripheral nervous system in ataxia telangiectasia.

Elucidating the Contribution of Skeletal Muscle Ion Channels to Amyotrophic Lateral Sclerosis in search of new therapeutic options

The discovery of pathogenetic mechanisms is essential to identify new therapeutic approaches in Amyotrophic Lateral Sclerosis (ALS). Here we investigated the role of the most important ion channels in skeletal muscle of an ALS animal model (MLC/SOD1^G93A) carrying a mutated SOD1 exclusively in this tissue, avoiding motor-neuron involvement. Ion channels are fundamental proteins for muscle function, and also to sustain neuromuscular junction and nerve integrity. By a multivariate statistical analysis, using machine learning algorithms, we identified the discriminant genes in MLC/SOD1^G93A mice. Surprisingly, the expression of ClC-1 chloride channel, present only in skeletal muscle, was reduced. Also, the expression of Protein Kinase-C, known to control ClC-1 activity, was increased, causing its inhibition. The functional characterization confirmed the reduction of ClC-1 activity, leading to hyperexcitability and impaired relaxation. The increased expression of ion channel coupled AMPA-receptor may contribute to sustained depolarization and functional impairment. Also, the decreased expression of irisin, a muscle-secreted peptide protecting brain function, may disturb muscle-nerve connection. Interestingly, the in-vitro application of chelerythrine or acetazolamide, restored ClC-1 activity and sarcolemma hyperexcitability in these mice. These findings show that ion channel function impairment in skeletal muscle may lead to motor-neuron increased vulnerability, and opens the possibility to investigate on new compounds as promising therapy.

A Novel Optical Tissue Clearing Protocol for Mouse Skeletal Muscle to Visualize Endplates in Their Tissue Context

Neuromuscular junctions (NMJs) mediate skeletal muscle contractions and play an important role in several neuromuscular disorders when their morphology and function are compromised. However, due to their small size and sparse distribution throughout the comparatively large, inherently opaque muscle tissue the analysis of NMJ morphology has been limited to teased fiber preparations, longitudinal muscle sections, and flat muscles. Consequently, whole mount analyses of NMJ morphology, numbers, their distribution, and assignment to a given muscle fiber have also been impossible to determine in muscle types that are frequently used in experimental paradigms. This impossibility is exacerbated by the lack of optical tissue clearing techniques that are compatible with clear and persistent NMJ stains. Here, we present MYOCLEAR, a novel and highly reproducible muscle tissue clearing protocol. Based on hydrogel-based tissue clearing methods, this protocol permits the labeling and detection of all NMJs in adult hindleg extensor digitorum longus muscles from wildtype and diseased mice. The method is also applicable to adult mouse diaphragm muscles and can be used for different staining agents, including toxins, lectins, antibodies, and nuclear dyes. It will be useful in understanding the distribution, morphological features, and muscle tissue context of NMJs in hindleg muscle whole mounts for biomedical and basic research.

Neuromuscular magnetic stimulation counteracts muscle decline in ALS patients: results of a randomized, double-blind, controlled study

The aim of the study was to verify whether neuromuscular magnetic stimulation (NMMS) improves muscle function in spinal-onset amyotrophic lateral sclerosis (ALS) patients. Twenty-two ALS patients were randomized in two groups to receive, daily for two weeks, NMMS in right or left arm (referred to as real-NMMS, rNMMS), and sham NMMS (sNMMS) in the opposite arm. All the patients underwent a median nerve conduction (compound muscle action potential, CMAP) study and a clinical examination that included a handgrip strength test and an evaluation of upper limb muscle strength by means of the Medical Research Council Muscle Scale (MRC). Muscle biopsy was then performed bilaterally on the flexor carpi radialis muscle to monitor morpho-functional parameters and molecular changes. Patients and physicians who performed examinations were blinded to the side of real intervention. The primary outcome was the change in the muscle strength in upper arms. The secondary outcomes were the change from baseline in the CMAP amplitudes, in the nicotinic ACh currents, in the expression levels of a selected panel of genes involved in muscle growth and atrophy, and in histomorphometric parameters of ALS muscle fibers. The Repeated Measures (RM) ANOVA with a Greenhouse-Geisser correction (sphericity not assumed) showed a significant effect [F(3, 63) = 5.907, p < 0.01] of rNMMS on MRC scale at the flexor carpi radialis muscle, thus demonstrating that the rNMMS significantly improves muscle strength in flexor muscles in the forearm. Secondary outcomes showed that the improvement observed in rNMMS-treated muscles was associated to counteracting muscle atrophy, down-modulating the proteolysis, and increasing the efficacy of nicotinic ACh receptors (AChRs). We did not observe any significant difference in pre- and post-stimulation CMAP amplitudes, evoked by median nerve stimulation. This suggests that the improvement in muscle strength observed in the stimulated arm is unlikely related to reinnervation. The real and sham treatments were well tolerated without evident side effects. Although promising, this is a proof of concept study, without an immediate clinical translation, that requires further clinical validation.

Histone deacetylase 4 protects from denervation and skeletal muscle atrophy in a murine model of amyotrophic lateral sclerosis

Background

Histone deacetylase 4 (HDAC4) has been proposed as a target for Amyotrophic Lateral Sclerosis (ALS) because it mediates nerve-skeletal muscle interaction and since its expression in skeletal muscle correlates with the severity of the disease. However, our recent studies on the skeletal muscle response upon long-term denervation highlighted the importance of HDAC4 in maintaining muscle integrity.

Methods

To fully identify the yet uncharacterized HDAC4 functions in ALS, we genetically deleted HDAC4 in skeletal muscles of a mouse model of ALS. Body weight, skeletal muscle, innervation and spinal cord were analyzed over time by morphological and molecular analyses. Transcriptome analysis was also performed to delineate the signaling modulated by HDAC4 in skeletal muscle of a mouse model of ALS.

Findings

HDAC4 deletion in skeletal muscle caused earlier ALS onset, characterized by body weight loss, muscle denervation and atrophy, and compromised muscle performance, although the main catabolic pathways were not activated. Transcriptome analysis identified the gene networks modulated by HDAC4 in ALS, revealing UCP1 as a top regulator that may be implicated in worsening ALS features.

Interpretation

HDAC4 plays an important role in preserving innervations and skeletal muscle in ALS, likely by modulating the UCP1 gene network. Our study highlights a possible risk in considering HDAC inhibitors for the treatment of ALS.

Fund

This work was supported by FIRB grant (RBFR12BUMH) from Ministry of Education, Universities and Research, by Fondazione Veronesi, by Sapienza research project 2017 (RM11715C78539BD8) and Polish National Science Center grant (UMO-2016/21/B/NZ3/03638).

Metabolic Changes Associated With Muscle Expression of SOD1G93A

Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disorder, classified into sporadic or familial forms and characterized by motor neurons death, muscle atrophy, weakness, and paralysis. Among the familial cases of ALS, approximately 20% are caused by dominant mutations in the gene coding for superoxide dismutase (SOD1) protein. Of note, mutant SOD1 toxicity is not necessarily limited to the central nervous system. ALS is indeed a multi-systemic and multifactorial disease that affects whole body physiology and induces severe metabolic changes in several tissues, including skeletal muscle. Nevertheless, whether alterations in the plasticity, heterogeneity, and metabolism of muscle fibers are the result of motor neuron degeneration or alternatively occur independently of it remain to be elucidated. To address this issue, we made use of a mouse model (MLC/SOD1^G93A) that overexpresses the SOD1 mutant gene selectively in skeletal muscle. We found an alteration in the metabolic properties of skeletal muscle characterized by alteration in fiber type composition and metabolism. Indeed, we observed an alteration of muscle glucose metabolism associated with the induction of Phosphofructokinases and Pyruvate dehydrogenase kinase 4 expression. The upregulation of Pyruvate dehydrogenase kinase 4 led to the inhibition of Pyruvate conversion into Acetyl-CoA. Moreover, we demonstrated that the MLC/SOD1^G93A transgene was associated with an increase of lipid catabolism and with the inhibition of fat deposition inside muscle fibers. All together these data demonstrate that muscle expression of the SOD1^G93A gene induces metabolic changes, along with a preferential use of lipid energy fuel by muscle fibers. We provided evidences that muscle metabolic alterations occurred before disease symptoms and independently of motor neuron degeneration, indicating that skeletal muscle is likely an important therapeutic target in ALS.

Smoke-induced neuromuscular junction degeneration precedes the fibre type shift and atrophy in chronic obstructive pulmonary disease

KEY POINTS

Chronic obstructive pulmonary disease (COPD) is largely caused by smoking, and patient limb muscle exhibits a fast fibre shift and atrophy. We show that this fast fibre shift is associated with type grouping, suggesting recurring cycles of denervation-reinnervation underlie the type shift. Compared to patients with normal fat-free mass index (FFMI), patients with low FFMI exhibited an exacerbated fibre type shift, marked accumulation of very small persistently denervated muscle fibres, and a blunted denervation-responsive transcript profile, suggesting failed denervation precipitates muscle atrophy in patients with low FFMI. Sixteen weeks of passive tobacco smoke exposure in mice caused neuromuscular junction degeneration, consistent with a key role for smoke exposure in initiating denervation in COPD.

ABSTRACT

A neurological basis for the fast fibre shift and atrophy seen in limb muscle of patients with chronic obstructive pulmonary disease (COPD) has not been considered previously. The objective of our study was: (1) to determine if denervation contributes to fast fibre shift and muscle atrophy in COPD; and (2) to assess using a preclinical smoking mouse model whether chronic tobacco smoke (TS) exposure could initiate denervation by causing neuromuscular junction (NMJ) degeneration. Vastus lateralis muscle biopsies were obtained from severe COPD patients [n = 10 with low fat-free mass index (FFMI), 65 years; n = 15 normal FFMI, 65 years) and healthy age- and activity-matched non-smoker control subjects (CON; n = 11, 67 years), to evaluate morphological and transcriptional markers of denervation. To evaluate the potential for chronic TS exposure to initiate these changes, we examined NMJ morphology in male adult mice following 16 weeks of passive TS exposure. We observed a high proportion of grouped fast fibres and a denervation transcript profile in COPD patients, suggesting that motor unit remodelling drives the fast fibre type shift in COPD patient limb muscle. A further exacerbation of fast fibre grouping in patients with low FFMI, coupled with blunted reinnervation signals, accumulation of very small non-specific esterase hyperactive fibres and neural cell adhesion molecule-positive type I and type II fibres, suggests denervation-induced exhaustion of reinnervation contributes to muscle atrophy in COPD. Evidence from a smoking mouse model showed significant NMJ degeneration, suggesting that recurring denervation in COPD is probably caused by decades of chronic TS exposure.

Exciting perspectives for Translational Myology in the Abstracts of the 2018Spring PaduaMuscleDays: Giovanni Salviati Memorial - Chapter IV - Abstracts of March 17, 2018

Myologists working in Padua (Italy) were able to continue a half-century tradition of studies of skeletal muscles, that started with a research on fever, specifically if and how skeletal muscle contribute to it by burning bacterial toxin. Beside main publications in high-impact-factor journals by Padua myologists, I hope to convince readers (and myself) of the relevance of the editing Basic and Applied Myology (BAM), retitled from 2010 European Journal of Translational Myology (EJTM), of the institution of the Interdepartmental Research Center of Myology of the University of Padova (CIR-Myo), and of a long series of International Conferences organized in Euganei Hills and Padova, that is, the PaduaMuscleDays. The 2018Spring PaduaMuscleDays (2018SpPMD), were held in Euganei Hills and Padua (Italy), in March 14-17, and were dedicated to Giovanni Salviati. The main event of the “Giovanni Salviati Memorial”, was held in the Aula Guariento, Accademia Galileiana di Scienze, Lettere ed Arti of Padua to honor a beloved friend and excellent scientist 20 years after his premature passing. Using the words of Prof. Nicola Rizzuto, we all share his believe that Giovanni “will be remembered not only for his talent and originality as a biochemist, but also for his unassuming and humanistic personality, a rare quality in highly successful people like Giovanni. The best way to remember such a person is to gather pupils and colleagues, who shared with him the same scientific interests and ask them to discuss recent advances in their own fields, just as Giovanni have liked to do”. Since Giovanni’s friends sent many abstracts still influenced by their previous collaboration with him, all the Sessions of the 2018SpPMD reflect both to the research aims of Giovanni Salviati and the traditional topics of the PaduaMuscleDays, that is, basics and applications of physical, molecular and cellular strategies to maintain or recover functions of skeletal muscles. The translational researches summarized in the 2018SpPMD Abstracts are at the appropriate high level to attract endorsement of Ethical Committees, the interest of International Granting Agencies and approval for publication in top quality international journals. The abstracts of the presentations of the March 16, 2018 Padua Muscle Day and those of the remaining Posters are listed in this chapter IV. The Author Index of the 2018Spring PaduaMuscleDays follows at page 78.

Targeting early PKCθ-dependent T-cell infiltration of dystrophic muscle reduces disease severity in a mouse model of muscular dystrophy

Chronic muscle inflammation is a critical feature of Duchenne muscular dystrophy and contributes to muscle fibre injury and disease progression. Although previous studies have implicated T cells in the development of muscle fibrosis, little is known about their role during the early stages of muscular dystrophy. Here, we show that T cells are among the first cells to infiltrate mdx mouse dystrophic muscle, prior to the onset of necrosis, suggesting an important role in early disease pathogenesis. Based on our comprehensive analysis of the kinetics of the immune response, we further identify the early pre-necrotic stage of muscular dystrophy as the relevant time frame for T-cell-based interventions. We focused on protein kinase C θ (PKCθ, encoded by Prkcq), a critical regulator of effector T-cell activation, as a potential target to inhibit T-cell activity in dystrophic muscle. Lack of PKCθ not only reduced the frequency and number of infiltrating T cells but also led to quantitative and qualitative changes in the innate immune cell infiltrate in mdx/Prkcq^-/- muscle. These changes were due to the inhibition of T cells, since PKCθ was necessary for T-cell but not for myeloid cell infiltration of acutely injured muscle. Targeting T cells with a PKCθ inhibitor early in the disease process markedly diminished the size of the inflammatory cell infiltrate and resulted in reduced muscle damage. Moreover, diaphragm necrosis and fibrosis were also reduced following treatment. Overall, our findings identify the early T-cell infiltrate as a therapeutic target and highlight the potential of PKCθ inhibition as a therapeutic approach to muscular dystrophy. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.