Search

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterized by the selective and progressive loss of motor neurons, leading to gradual paralysis and death within 2 to 5 years after diagnosis. The exact underlying pathogenic mechanism(s) remain elusive. This is particularly the case for sporadic ALS (sALS), representing 90 % of cases, as modelling a sporadic disease is extremely difficult. We used human induced pluripotent stem cell (hiPSC)-derived motor neurons from sALS patients to investigate early disease mechanisms. The earliest phenotype that we observed were profound axonal defects including impaired axonal transport, defective axonal outgrowth and a reduced formation of neuromuscular junctions. Transcriptomic profiling revealed significant dysregulation in axon guidance pathways, with upregulation of specific axonal regeneration-inhibiting genes, such as EphA4 and DCC in sALS motor neurons. Our findings suggest that dysregulation of axon guidance pathways contributes to axonal defects and that this could play a crucial role in the pathogenesis of sALS., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: L.V.D.B. is head of the Scientific Advisory Board of Augustine Therapeutics (Leuven, Belgium) and is part of the Investment Advisory Board of Droia Ventures (Meise, Belgium)., (Copyright © 2025 The Authors. Published by Elsevier Inc. All rights reserved.)

Aims: Peripheral artery disease (PAD) reduces blood flow to the legs and causes severe muscle and leg dysfunction for PAD patients. Skeletal muscle contractile function is dependent on the health of the muscle itself and that of the neuromuscular junction (NMJ) on the muscle membrane., Methods: To determine whether the NMJ, including the motor nerve terminals and nicotinic acetylcholine receptors (nAChR), is damaged in PAD, gastrocnemius muscles were collected from 3 controls and 13 PAD patients to capture images from 331 control NMJs and 512 PAD NMJs., Results: For the motor nerve terminals, there were more denervated nAChR clusters and fewer nerve terminal occupancies in NMJs in PAD patients, compared with controls. For the nAChR clusters in the NMJs, the area per nAChR cluster was 369.3 ± 6.7 versus 225.2 ± 5.3 μm 2 , the area per fragment was 195.9 ± 9.2 versus 107.1 ± 3.1 μm 2 , the number of fragments per nAChR cluster was 2.3 ± 0.1 versus 3.2 ± 0.1, the nAChR cluster area per endplate area was 75.7 ± 1.6 versus 55.7 ± 1.1%, total distance of fragments per nAChR cluster was 4.6 ± 0.4 versus 8.8 ± 0.8 μm, and the fragmented nAChR clusters were 7.6% versus 21.6% of total nAChR clusters in controls versus PAD patients, respectively (p < 0.05 in all parameters)., Conclusions: Our data demonstrate deterioration of the motor nerve terminals and nAChR clusters, which may compromise neuromuscular transmission, and contribute to the severe leg dysfunction observed in patients with PAD., (© 2025 The Author(s). Neuropathology and Applied Neurobiology published by John Wiley & Sons Ltd on behalf of British Neuropathological Society.)

One of the most critical factors impacting healthspan in the elderly is the loss of muscle mass and function, clinically referred to as sarcopenia. Muscle atrophy and weakness lead to loss of mobility, increased risk of injury, metabolic changes and loss of independence. Thus, defining the underlying mechanisms of sarcopenia is imperative to enable the development of effective interventions to preserve muscle function and quality in the elderly and improve healthspan. Over the past few decades, understanding the roles of mitochondrial dysfunction and oxidative stress has been a major focus of studies seeking to reveal critical molecular pathways impacted during aging. In this review, we will highlight how oxidative stress might contribute to sarcopenia by discussing the impact of oxidative stress on the loss of innervation and alteration in the neuromuscular junction (NMJ), on muscle mitochondrial function and atrophy pathways, and finally on muscle contractile function., Competing Interests: Declaration of competing interest A statement is included on the tile page declaring no competing interests., (Published by Elsevier Inc.)

Duchenne muscular dystrophy (DMD) is caused by the absence of the full form of the dystrophin protein, which is essential for maintaining the structural integrity of muscle cells, including those in the heart and respiratory system. Despite progress in understanding the molecular mechanisms associated with DMD, myocardial insufficiency persists as the primary cause of mortality, and existing therapeutic strategies remain limited. This study investigates the hypothesis that a dysregulation of the biological communication between infiltrating macrophages (MPs) and neurocardiac junctions exists in dystrophic cardiac tissue. In a mouse model of DMD (mdx), this phenomenon is influenced by the over-release of chondroitin sulfate proteoglycan-4 (CSPG4), a key inhibitor of nerve sprouting and a modulator of the neural function, by MPs infiltrating the cardiac tissue and associated with dilated cardiomyopathy, a hallmark of DMD. Givinostat, the histone deacetylase inhibitor under current development as a clinical treatment for DMD, is effective at both restoring a physiological microenvironment at the neuro-cardiac junction and cardiac function in mdx mice in addition to a reduction in cardiac fibrosis, MP-mediated inflammation, and tissue CSPG4 content. This study provides novel insight into the pathophysiology of DMD in the heart, identifying potential new biological targets. © 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland., (© 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.)

Cytoplasmic dynein 1, a motor protein essential for retrograde axonal transport, is increasingly implicated in the pathogenesis of neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). In this study, we developed a novel mouse model that combines the Legs at odd angles (Loa, F580Y) point mutation in the dynein heavy chain with a cholinergic neuron-specific knockout of the dynein heavy chain. This model, for the first time, allows us to investigate the impact of Loa allele exclusivity in these neurons into adulthood. Our findings reveal that this selective increase in dynein dysfunction exacerbated the phenotypes observed in heterozygous Loa mice including pre-wean survival, reduced body weight and grip strength. Additionally, it induced ALS-like pathology in neuromuscular junctions (NMJs) not seen in heterozygous Loa mice. Notably, we also found a previously unobserved significant increase in neurons displaying TDP-43 puncta in both Loa mutants, suggesting early TDP-43 mislocalisation - a hallmark of ALS. The novel model also exhibited a concurrent rise in p62 puncta that did not co-localise with TDP-43, indicating broader impairments in autophagic clearance mechanisms. Overall, this new model underscores the fact that dynein impairment alone can induce ALS-like pathology and provides a valuable platform to further explore the role of dynein in ALS., Competing Interests: Declaration of competing interest The author EC holds shares in Thermo Fisher Scientific and various index funds which may include companies whose products were used in the research reported in this article. Additionally, EC has been engaged in a compensated collaboration with Thermo Fisher Scientific for promotional activities unrelated to this research. These potential financial interests do not influence the design, execution, or interpretation of the research findings presented in this article. All other authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Amyotrophic lateral sclerosis (ALS) is the most prevalent motor neuron disease in adults. Currently, there are no known drugs or clinical approaches that have demonstrated efficacy in treating ALS. Mitochondrial function and autophagy have been identified as crucial mechanisms in the development of ALS. While Bax inhibitor 1 (BI1) has been implicated in neurodegenerative diseases, its exact mechanism remains unknown. This study investigates the therapeutic impact of BI1 overexpression on ALS both in vivo and in vitro, revealing its ability to mitigate SOD1 G93A -induced apoptosis, nuclear damage, mitochondrial dysfunction, and axonal degeneration of motor neurons. At the same time, BI1 prolongs onset time and lifespan of ALS mice, improves motor function, and alleviates neuronal damage, muscle damage, neuromuscular junction damage among other aspects. The findings indicate that BI1 can inhibit pathological TDP43 morphology and initially stimulate autophagy through interaction with TDP43. This study establishes a solid theoretical foundation for understanding the regulation of autophagy by BI1 and TDP43 while shedding light on the pathogenesis of ALS through their interaction - offering new concepts and targets for clinical implementation and drug development., Competing Interests: Declarations. Ethics Approval and Consent to Participate: All animal experiments comply with the National Institutes of Health guide for the care and use of Laboratory animals (NIH Publications No. 8023, revised 1996) and approval from the Institutional Animal Care and Use Committee of Jilin University. Consent for Publication: Not applicable. Competing Interests: The authors declare no competing interests., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The development of ground-breaking Survival Motor Neuron (SMN) replacement strategies has revolutionized the field of Spinal Muscular Atrophy (SMA) research. However, the limitations of these therapies have now become evident, highlighting the need for the development of complementary targets beyond SMN replacement. To address these challenges, here we explored, in in vitro and in vivo disease models, Stathmin-2 (STMN2), a neuronal microtubule regulator implicated in neurodegenerative diseases like Amyotrophic Lateral Sclerosis (ALS), as a novel SMN-independent target for SMA therapy. Our findings revealed that STMN2 overexpression effectively restored axonal growth and outgrowth defects in induced pluripotent stem cell-(iPSC)-derived motor neurons (MNs) from SMA patients. Intracerebroventricular administration of adeno-associated virus serotype 9 (AAV9) carrying Stmn2 cDNA significantly ameliorated survival rates, motor functions, muscular and neuromuscular junction pathological features in SMA mice, mirrored by in vitro outcomes. Overall, this pioneering study not only provides insight into the therapeutic potential of STMN2 in SMA, but also suggests its broader applications for MN diseases, marking a substantial step forward in addressing the multifaceted challenges of neurological diseases treatment., Competing Interests: Declarations. Ethical approval: All animal experiments strictly follow the guidelines of the Italian Ministry of Health in compliance with U.S. National Institutes of Health Guide for the Care and Use of Laboratory Animals (718/2022). Consent for publication: All the authors have approved and agreed to publish this manuscript. Conflict of interest: The authors declare that they have no conflicts of interest., (© 2024. The Author(s).)

The muscle-specific microRNA miR-206 has recently emerged as a potential regulator of genes involved in the formation and regeneration of the neuromuscular junction (NMJ). This study investigated miR-206-3p (miR-206) expression in synaptic and non-synaptic regions of denervated mice and α-dystrobrevin (Dtna)-knockout mice, as well as its impact on the formation and/or maintenance of agrin-induced acetylcholine receptor (AChR) clusters. In denervated, Dtna-deficient and crushed muscles, miR-206 expression significantly increased compared to what was seen for innervated muscles. Although miR-206 expression was slightly elevated in the synaptic regions of innervated muscles, it was dramatically increased in non-synaptic areas of denervated muscles. miR-206 targets transcripts of essential NMJ proteins, such as Dtna, α-syntrophin (Snta1) and rapsyn, but not the AChRα subunit (encoded by Chrna1) or Lrp4 in innervated muscles. However, in denervated muscles, AChRα transcripts, which increased significantly, become a target of miR-206. Co-expression of miR-206 with rapsyn, Dtna and Snta1 in C2C12 myoblasts significantly reduced their protein levels, and overexpression of miR-206 in myotubes disrupted agrin-induced AChR clustering. These results indicate that miR-206 fine-tunes NMJ signaling proteins by regulating transcripts of various proteins with different localizations under normal and pathological conditions., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Inactivity and ageing can have a detrimental impact on skeletal muscle and the neuromuscular junction (NMJ). Decreased physical activity results in muscle atrophy, impaired mitochondrial function, and NMJ instability. Ageing is associated with a progressive decrease in muscle mass, deterioration of mitochondrial function in the motor axon terminals and in myofibres, NMJ instability and loss of motor units. Focusing on the impact of inactivity and ageing, this review examines the consequences on NMJ stability and the role of mitochondrial dysfunction, delving into their complex relationship with ageing and disuse. Evidence suggests that mitochondrial dysfunction can be a pathogenic driver for NMJ alterations, with studies revealing the role of mitochondrial defects in motor neuron degeneration and NMJ instability. Two perspectives behind NMJ instability are discussed: one is that mitochondrial dysfunction in skeletal muscle triggers NMJ deterioration, the other envisages dysfunction of motor terminal mitochondria as a primary contributor to NMJ instability. While evidence from these studies supports both perspectives on the relationship between NMJ dysfunction and mitochondrial impairment, gaps persist in the understanding of how mitochondrial dysfunction can cause NMJ deterioration. Further research, both in humans and in animal models, is essential for unravelling the mechanisms and potential interventions for age- and inactivity-related neuromuscular and mitochondrial alterations., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Peripheral nerve-crush injury is a well-established model of neuromuscular junction (NMJ) denervation and subsequent re-innervation. Functionally, the skeletal muscle follows a similar pattern as neural recovery, with immediate loss of force production that steadily improves in parallel with rates of re-innervation. On the other hand, traumatic injury to the muscle itself, specifically volumetric muscle loss (VML), results in an irrecoverable loss of muscle function. Recent work has indicated significant impairments to the NMJ following this injury that appear chronic in nature, alongside the lack of functional recovery. Thus, the goal of this study was to compare the effects of nerve and muscle injury on NMJ remodeling. Even numbers of adult male and female mice were used with three experimental groups: injury Naïve, nerve crush, and VML injury; and three terminal timepoints: 3-, 48-, and 112-days post-injury. Confirming the assumed recoverability of the two injury models, we found in vivo maximal torque was fully restored following nerve-crush injury but remained at a significant deficit following VML. Compared to injury Naïve and nerve-crush injury, we found VML results in aberrantly high trophic signaling (e.g., neuregulin-1) and numbers of supporting cells, including terminal Schwann cells and sub-synaptic nuclei. In some cases, sex differences were detected, including higher rates of innervation in females than males. Both nerve crush and VML injury display chronic changes to NMJ morphology, such as increased fragmentation and nerve sprouting, highlighting the potential of VML for modeling NMJ regeneration in adulthood, alongside the established nerve-injury models., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Mutations in the nuclear-encoded mitochondrial gene CHCHD10 have been observed in patients with a spectrum of diseases that include amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). To investigate the pathogenic nature of disease-associated variants of CHCHD10 we generated a zebrafish knock-in (KI) model expressing the orthologous ALS-associated CHCHD10 P80L variant (zebrafish: Chchd10 P83L ). Larval chchd10 P83L/P83L fish displayed reduced Chchd10 protein expression levels, motor impairment, reduced survival and abnormal neuromuscular junctions (NMJ). These deficits were not accompanied by changes in transcripts involved in the integrated stress response (ISR), phenocopying previous findings in our knockout (chchd10 -/- ). Adult, 11-month old chchd10 P83L/P83L zebrafish, displayed smaller slow- and fast-twitch muscle cell cross-sectional areas compared to wild type zebrafish muscle cells. Motoneurons in the spinal cord of chchd10 P83L/P83L zebrafish displayed similar cross-sectional areas to that of wild type motor neurons and significantly fewer motor neurons were observed when compared to chchd2 -/- adult spinal cords. Bulk RNA sequencing using whole spinal cords of 7-month old fish revealed transcriptional changes associated with neuroinflammation, apoptosis, amino acid metabolism and mt-DNA inflammatory response in our chchd10 P83L/P83L model. The findings presented here, suggest that the CHCHD10 P80L variant confers an ALS-like phenotype when expressed in zebrafish., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

We aimed to evaluate whether inherited mitochondrial dysfunction is associated with neuromuscular junction remodeling in patients with mitochondrial disorders. Muscle biopsies from 15 patients with mitochondrial disorders and 10 control patients were analyzed through immunostaining for various neuromuscular junction components. The patient group, with a mean age of 49.9 years, exhibited various mitochondrial disorders including chronic progressive external ophthalmoplegia, Kearns-Sayre syndrome, and mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes. Patients with mitochondrial disorders had a high percentage of remodeled (p= 0.0001), neoformed (p= 0.0049) and dilated (p= 0.016) endplates. There was a trend toward an increased proportion of neuromuscular junctions with terminal Schwann cell extension in these patients (p= 0.052). No significant difference was found in myofiber diameter between the groups. The observed neuromuscular junction defects varied widely across different mitochondrial disorder phenotypes and were present even without accompanying muscle weakness or neuropathy. This suggest that mitochondrial disorders are associated with a primary NMJ remodeling independent of muscle structural damage. Pathomechanisms underpinning this remodeling of the neuromuscular junction, as well as clinical factors predictive of this remodeling, remain to be fully characterized., Competing Interests: Declaration of competing interest The authors report no competing interests relevant to the manuscript, the authors have no relevant financial or non-financial interests to disclose. Human biological samples and associated data were obtained from TTK Biobank (CRB-HCL Hospices Civils de Lyon BB-0033-00046). All tissue samples were obtained according to French Legislation and written informed consent was obtained from patients for all samples. TTK is authorized by the French Ministry of Social Affairs and Health (DC2015-2566) with transfer authorization (AC 2015-2576). The Biobank database is registered in the national data protection commission (Commission Nationale Informatique et Libertés). Funding for this work was obtained from AFM telethon through the strategic MyoNeurALP alliance, the Fondation pour la Recherche Médicale through an “équipe FRM” funding to L.S., (Copyright © 2024. Published by Elsevier B.V.)

Background: Spinal Muscular Atrophy (SMA) is an inherited neurodegenerative disease caused by the loss or mutation of the survival motor neuron 1 (SMN1 ) gene. Though classically regarded as a motor neuron disorder, reports are increasingly describing the involvement of non-neuronal organs in SMA. The Smn 2B/- mouse is a model of SMA that displays a peripheral phenotype including metabolic defects., Objective: Here, we characterized several neuronal and non-neuronal defects in the Smn 2B/- mouse throughout development to better understand the progression of the disease and the relationship between tissue defects., Methods: We collected tissues from mutant Smn 2B/- mice and Smn 2B/+ littermate controls at several timepoints and evaluated spinal cord motor neuron loss, neuromuscular junction pathology, muscle fiber size, liver steatosis, and pancreatic islet cell composition. Blood glucose and plasma neurofilament light chain (NfL) were also measured., Results: Smn 2B/- mice displayed several peripheral defects prior to motor neuron loss and showed early elevations in neurofilament light chain (NfL) protein., Conclusions: This work provides an important framework for guiding future research with this mouse model and demonstrates that the liver may be an early target in the development of SMA.

As a widespread global issue, protein deficiency hinders development and optimal growth in offspring. Maternal low-protein diet influences the development of age-related diseases, including sarcopenia, by altering the epigenome and organ structure through potential increase in oxidative stress. However, the long-term effects of lactational protein restriction or postnatal lifelong protein restriction on the neuromuscular system have yet to be elucidated. Our results demonstrated that feeding a normal protein diet after lactational protein restriction did not have significant impacts on the neuromuscular system in later life. In contrast, a lifelong low-protein diet induced a denervation phenotype and led to demyelination in the sciatic nerve, along with an increase in the number of centralised nuclei and in the gene expression of atrogenes at 18 months of age, indicating an induced skeletal muscle atrophy. These changes were accompanied by an increase in proteasome activity in skeletal muscle, with no significant alterations in oxidative stress or mitochondrial dynamics markers in skeletal muscle later in life. Thus, lifelong protein restriction may induce skeletal muscle atrophy through changes in peripheral nerves and neuromuscular junctions, potentially contributing to the early onset or exaggeration of sarcopenia., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Degeneration of the motoneuron and neuromuscular junction (NMJ) and loss of motor units (MUs) contribute to age-related muscle wasting and weakness associated with sarcopenia. However, these features have not been comprehensively investigated in humans. This study aimed to compare neuromuscular system integrity and function at different stages of sarcopenia, with a particular focus on NMJ stability and MU properties., Methods: We recruited 42 young individuals (Y) (aged 25.98 ± 4.6 years; 57% females) and 88 older individuals (aged 75.9 ± 4.7 years; 55% females). The older group underwent a sarcopenia screening according to the revised guidelines of the European Working Group on Sarcopenia in Older People 2. In all groups, knee extensor muscle force was evaluated by isometric dynamometry, muscle morphology by ultrasound and MU potential properties by intramuscular electromyography (iEMG). MU number estimate (iMUNE) and blood samples were obtained. Muscle biopsies were collected in a subgroup of 16 Y and 52 older participants., Results: Thirty-nine older individuals were non-sarcopenic (NS), 31 pre-sarcopenic (PS) and 18 sarcopenic (S). A gradual decrease in quadriceps force, cross-sectional area and appendicular lean mass was observed across the different stages of sarcopenia (for all P < 0.0001). Handgrip force and the Short Physical Performance Battery score also showed a diminishing trend. iEMG analyses revealed elevated near fibre segment jitter in NS, PS and S compared with Y (Y vs. NS and S: P < 0.0001; Y vs. PS: P = 0.0169), suggestive of age-related impaired NMJ transmission. Increased C-terminal agrin fragment (P < 0.0001) and altered caveolin 3 protein expression were consistent with age-related NMJ instability in all the older groups. The iMUNE was lower in all older groups (P < 0.0001), confirming age-related loss of MUs. An age-related increase in MU potential complexity was also observed. These observations were accompanied by increased muscle denervation and axonal damage, evinced by the increase in neural cell adhesion molecule-positive fibres (Y vs. NS: P < 0.0001; Y vs. S: P = 0.02) and the increase in serum concentration of neurofilament light chain (P < 0.0001), respectively. Notably, most of these MU and NMJ parameters did not differ when comparing older individuals with or without sarcopenia., Conclusions: Alterations in MU properties, axonal damage, an altered innervation profile and NMJ instability are prominent features of the ageing of the neuromuscular system. These neuromuscular alterations are accompanied by muscle wasting and weakness; however, they appear to precede clinically diagnosed sarcopenia, as they are already detectable in older NS individuals., (© 2024 The Author(s). Journal of Cachexia, Sarcopenia and Muscle published by Wiley Periodicals LLC.)

In human Alzheimer's disease (AD), the aggregation of tau protein is considered a significant hallmark, along with amyloid-beta. The formation of neurofibrillary tangles due to aberrant phosphorylation of tau disrupts microtubule stability, leading to neuronal toxicity, dysfunction, and subsequent cell death. Nesfatin-1 is a neuropeptide primarily known for regulating appetite and energy homeostasis. However, the function of Nesfatin-1 in a neuroprotective role has not been investigated. In this study, we aimed to elucidate the effect of Nesfatin-1 on tau pathology using the Drosophila model system. Our findings demonstrate that Nesfatin-1 effectively mitigates the pathological phenotypes observed in Drosophila human Tau overexpression models. Nesfatin-1 overexpression rescued the neurodegenerative phenotypes in the adult fly's eye and bristle. Additionally, Nesfatin-1 improved locomotive behavior, neuromuscular junction formation, and lifespan in the hTau AD model. Moreover, Nesfatin-1 controls tauopathy by reducing the protein level of hTau. Overall, this research highlights the potential therapeutic applications of Nesfatin-1 in ameliorating the pathological features associated with Alzheimer's disease., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Lafora disease (LD), a fatal neurodegenerative disorder, is caused by mutations in the EPM2A gene encoding laforin phosphatase or NHLRC1 gene encoding malin ubiquitin ligase. LD symptoms include epileptic seizures, ataxia, dementia and cognitive decline. Studies on LD have primarily concentrated on the pathophysiology in the brain. A few studies have reported motor symptoms, muscle weakness and muscle atrophy. Intriguingly, skeletal muscles are known to accumulate Lafora polyglucosan bodies. Using laforin-deficient mice, an established model for LD, we demonstrate that LD pathology correlated with structural and functional impairments in the neuromuscular junction (NMJ). Specifically, we found impairment in NMJ transmission, which coincided with altered expression of NMJ-associated genes and reduced motor endplate area, fragmented junctions and loss of fully innervated junctions at the NMJ. We also observed a reduction in alpha-motor neurons in the lumbar spinal cord, with significant presynaptic morphological alterations. Disorganised myofibrillar patterns, slight z-line streaming and muscle atrophy were also evident in LD animals. In summary, our study offers insight into the neuropathic and myopathic alterations leading to motor deficits in LD., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disease characterized by the progressive destruction of the neuromuscular junction (NMJ) and the degeneration of motor neurons, eventually leading to atrophy and paralysis of voluntary muscles responsible for motion and breathing. NMJs, synaptic connections between motor neurons and skeletal muscle fibers, are extremely fragile in ALS. To determine the effects of early electroacupuncture (EA) intervention on nerve reinnervation and regeneration following injury, a model of sciatic nerve injury (SNI) was first established using SOD1 G93A mice, and early electroacupuncture (EA) intervention was conducted at Baihui (DU20), and bilateral Zusanli (ST36). The results revealed that EA increased the Sciatic nerve Functional Index, the structural integrity of the gastrocnemius muscles, and the cross-sectional area of muscle fibers, as well as up-regulated the expression of acetylcholinesterase and facilitated the co-location of α7 nicotinic acetate choline receptors and α-actinin. Overall, these results suggested that EA can promote the repair and regeneration of injured nerves and delay NMJ degeneration in SOD1 G93A -SNI mice. Moreover, analysis of the cerebral cortex demonstrated that EA alleviated cortical motor neuron damage in SOD1 G93A mice, potentially attributed to the inhibition of the cyclic GMP-AMP synthase-stimulator of interferon genes pathway and the release of interferon-β suppressing the activation of natural killer cells and the secretion of interferon-γ, thereby further inhibiting microglial activation and the expression of inflammatory factors. In summary, EA delayed the degeneration of NMJ and mitigated the loss of cortical motor neurons, thus delaying disease onset, accompanied by alleviation of muscle atrophy and improvements in motor function in SOD1 G93A mice., Competing Interests: Declaration of Competing Interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

PURA syndrome is caused by heterozygous de novo pathogenic variants in PURA. It is characterized by moderate to severe neurodevelopmental disability with a wide clinical spectrum and an evolving phenotype. We present two individuals with genetically confirmed PURA syndrome who had severe neonatal signs and symptoms and a novel phenotype suggestive of neuromuscular junction pathology. We demonstrate that PURA syndrome shares features consistent with a congenital myasthenic syndrome; we thus recommend electrodiagnostic study in neonates and infants with PURA syndrome, and consideration of salbutamol as a therapeutic option. [ABSTRACT FROM AUTHOR]

Muscle-specific kinase (MuSK) is essential for the formation, function, and preservation of neuromuscular synapses. Activation of MuSK by a MuSK agonist antibody may stabilize or improve the function of the neuromuscular junction (NMJ) in patients with disorders of the NMJ, such as congenital myasthenia (CM). Here, we generated and characterized ARGX-119, a first-in-class humanized agonist monoclonal antibody specific for MuSK, that is being developed for treatment of patients with neuromuscular diseases. We performed in vitro ligand-binding assays to show that ARGX-119 binds with high affinity to the Frizzled-like domain of human, nonhuman primate, rat, and mouse MuSK, without off-target binding, making it suitable for clinical development. Within the Fc region, ARGX-119 harbors L234A and L235A mutations to diminish potential immune-activating effector functions. Its mode of action is to activate MuSK, without interfering with its natural ligand neural Agrin, and cluster acetylcholine receptors in a dose-dependent manner, thereby stabilizing neuromuscular function. In a mouse model of DOK7 CM, ARGX-119 prevented early postnatal lethality and reversed disease relapse in adult Dok7 CM mice by restoring neuromuscular function and reducing muscle weakness and fatigability in a dose-dependent manner. Pharmacokinetic studies in nonhuman primates, rats, and mice revealed a nonlinear PK behavior of ARGX-119, indicative of target-mediated drug disposition and in vivo target engagement. On the basis of this proof-of-concept study, ARGX-119 has the potential to alleviate neuromuscular diseases hallmarked by impaired neuromuscular synaptic function, warranting further clinical development.

Local tetanus develops when limited amounts of tetanus neurotoxin (TeNT) are released by Clostridium tetani generated from spores inside a necrotic wound. Within days, a spastic paralysis restricted to the muscles of the affected anatomical area develops. This paralysis follows the retrograde transport of TeNT inside the axons of motoneurons and its uptake by inhibitory interneurons with cleavage of a vesicle-associated membrane protein required for neurotransmitter release. Consequently, incontrollable excitation of motoneurons causes contractures of innervated muscles and leads to local spastic paralysis. Here, the initial events occurring close to the site of TeNT release were investigated in a mouse model of local tetanus. A peripheral flaccid paralysis was found to occur, before or concurrent to the spastic paralysis. At variance from the confined TeNT proteolytic activity taking place within motor neuron terminals, central protein cleavage was detected within inhibitory interneurons controlling motor neuron efferents innervating muscle groups distant from the site of TeNT release. These results indicate peripheral activity of TeNT in tetanus and explains why the spastic paralysis observed in local tetanus, although confined to single limbs, generally affects multiple muscles. The initial TeNT neuroparalytic activity can be detected by measuring the compound muscle action potential, providing a very early diagnosis and therapy, thus preventing the ensuing life-threatening generalized tetanus., (Copyright © 2024 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Amyotrophic lateral sclerosis (ALS) is a devastating paralytic disorder caused by the death of motoneurons. Several mutations in the KIF5A gene have been identified in patients with ALS. Some mutations affect the splicing sites of exon 27 leading to its deletion (Δ27 mutation). KIF5A Δ27 is aggregation-prone and pathogenic for motoneurons due to a toxic gain of function. Another mutation found to be enriched in ALS patients is a proline/leucine substitution at position 986 (P986L mutation). Bioinformatic analyses strongly suggest that this variant is benign. Our study aims to conduct functional studies in Drosophila to classify the KIF5A P986L variant. When expressed in motoneurons, KIF5A P986L does not modify the morphology of larval NMJ or the synaptic transmission. In addition, KIF5A P986L is uniformly distributed in axons and does not disturb mitochondria distribution. Locomotion at larval and adult stages is not affected by KIF5A P986L. Finally, both KIF5A WT and P986L expression in adult motoneurons extend median lifespan compared to control flies. Altogether, our data show that the KIF5A P986L variant is not pathogenic for motoneurons and may represent a hypomorphic allele, although it is not causative for ALS., (© 2024. The Author(s).)

Triosephosphate isomerase deficiency (TPI Df) is a rare multisystem disorder with severe neuromuscular symptoms which arises exclusively from mutations within the TPI1 gene. Studies of TPI Df have been limited due to the absence of mammalian disease models and difficulties obtaining patient samples. Recently, we developed a novel murine model of TPI Df which models the most common disease-causing mutation in humans, TPI1 E105D . Using our model in the present study, the underlying pathogenesis of neuromuscular symptoms has been elucidated. This is the first report detailing studies of neuromuscular pathology within a murine model of TPI Df. We identified several contributors to neuromuscular symptoms, including neurodegeneration in the brain, alterations in neurotransmission at the neuromuscular junction, and reduced muscle fiber size. TPI Df mice also exhibited signs of cardiac pathology and displayed a deficit in vascular smooth muscle functionality. Together, these findings provide insight into pathogenesis of the neuromuscular symptoms in TPI Df and can guide the future development of therapeutics., (© 2024. The Author(s).)

We investigated the shuttling of Homer protein isoforms identified in soluble (cytosolic) vs. insoluble (membrane-cytoskeletal) fraction and Homer protein-protein interaction/activation in the deep postural calf soleus ( SOL) and non-postural gastrocnemius ( GAS ) muscles of het -/- mice, i.e., mice with an autosomal recessive variant responsible for a vestibular disorder, in order to further elucidate a) the underlying mechanisms of disrupted vestibular system-derived modulation on skeletal muscle, and b) molecular signaling at respective neuromuscular synapses. Heterozygote mice muscles served as the control (CTR). An increase in Homer cross-linking capacity was present in the SOL muscle of het -/- mice as a compensatory mechanism for the altered vestibule system function. Indeed, in both fractions, different Homer immunoreactive bands were detectable, as were Homer monomers (~43-48 kDa), Homer dimers (~100 kDa), and several other Homer multimer bands (>150 kDA). The het -/- GAS particulate fraction showed no Homer dimers vs. SOL . The het -/- SOL soluble fraction showed a twofold increase (+117%, p ≤ 0.0004) in Homer dimers and multimers. Homer monomers were completely absent from the SOL independent of the animals studied, suggesting muscle-specific changes in Homer monomer vs. dimer expression in the postural SOL vs. the non-postural GAS muscles. A morphological assessment showed an increase (+14%, p ≤ 0.0001) in slow/type-I myofiber cross-sectional area in the SOL of het -/- vs. CTR mice. Homer subcellular immuno-localization at the neuromuscular junction (NMJ) showed an altered expression in the SOL of het -/- mice, whereas only not-significant changes were found for all Homer isoforms, as judged by RT-qPCR analysis. Thus, muscle-specific changes, myofiber properties, and neuromuscular signaling mechanisms share causal relationships, as highlighted by the variable subcellular Homer isoform expression at the instable NMJs of vestibular lesioned het -/- mice.

Duchenne muscular dystrophy (DMD) is the most common X-linked disease. DMD is caused by a lack of dystrophin, a critical structural protein in striated muscle. Dystrophin deficiency leads to inflammation, fibrosis, and muscle atrophy. Boys with DMD have progressive muscle weakness within the diaphragm that results in respiratory failure in the 2nd or 3rd decade of life. The most common DMD mouse model - the mdx mouse - is not sufficient for evaluating genetic medicines that specifically target the human DMD (hDMD) gene sequence. Therefore, a novel transgenic mouse carrying the hDMD gene with an exon 52 deletion was created (hDMDΔ52;mdx). We characterized the respiratory function and pathology in this model using whole body plethysmography, histology, and immunohistochemistry. At 6-months-old, hDMDΔ52;mdx mice have reduced maximal respiration, neuromuscular junction pathology, and fibrosis throughout the diaphragm, which worsens at 12-months-old. In conclusion, the hDMDΔ52;mdx exhibits moderate respiratory pathology, and serves as a relevant animal model to study the impact of novel genetic therapies, including gene editing, on respiratory function., Competing Interests: Declaration of Competing Interest CAG is an advisor to Sarepta Therapeutics and an advisor and co-founder of Tune Therapeutics. CAG and JRH are inventors on patents and patent applications related to genome editing. AMB is an employee and stakeholder of Fulcrum Therapuetics., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Background: Alzheimer's disease (AD) impairs cognitive functions and peripheral systems, including skeletal muscles. The PS19 mouse, expressing the human tau P301S mutation, shows cognitive and muscular pathologies, reflecting the central and peripheral atrophy seen in AD., Methods: We analysed skeletal muscle morphology and neuromuscular junction (NMJ) through immunohistochemistry and advanced image quantification. A factorial Analysis of Variance assessed muscle weight, NCAM expression, NMJ, myofibre type distribution, cross-sectional areas, expression of single or multiple myosin heavy-chain isoforms, and myofibre grouping in PS19 and wild type (WT) mice over their lifespan (1-12 months)., Results: Significant weight differences in extensor digitorum longus (EDL) and soleus muscles between WT and PS19 mice were noted by 7-8 months. For EDL muscle in females, WT weighed 0.0113 ± 0.0005 compared with PS19's 0.0071 ± 0.0008 (P < 0.05), and in males, WT was 0.0137 ± 0.0001 versus PS19's 0.0069 ± 0.0006 (P < 0.005). Similarly, soleus muscle showed significant differences; females (WT: 0.0084 ± 0.0004; PS19: 0.0057 ± 0.0005, P < 0.005) and males (WT: 0.0088 ± 0.0003; PS19: 0.0047 ± 0.0004, P < 0.0001). Analysis of the NMJ in PS19 mice revealed a marked reduction in myofibre innervation at 5 months, with further decline by 10 months. NMJ pre-terminals in PS19 mice became shorter and simpler by 5 months, showing a steep decline by 10 months. Genotype and age strongly influenced muscle NCAM immunoreactivity, denoting denervation as early as 5-6 months in EDL muscle Type II fibres, with earlier effects in soleus muscle Type I and II fibres at 3-4 months. Muscle denervation and subsequent myofibre atrophy were linked to a reduction in Type IIB fibres in the EDL muscle and Type IIA fibres in the soleus muscle, accompanied by an increase in hybrid fibres. The EDL muscle showed Type IIB fibre atrophy with WT females at 1505 ± 110 μm 2 versus PS19's 1208 ± 94 μm 2 , and WT males at 1731 ± 185 μm 2 versus PS19's 1227 ± 116 μm 2 . Similarly, the soleus muscle demonstrated Type IIA fibre atrophy from 5 to 6 months, with WT females at 1194 ± 52 μm 2 versus PS19's 858 ± 62 μm 2 , and WT males at 1257 ± 43 μm 2 versus PS19's 1030 ± 55 μm 2 . Atrophy also affected Type IIX, I + IIA, and IIA + IIX fibres in both muscles. The timeline for both myofibre and overall muscle atrophy in PS19 mice was consistent, indicating a simultaneous decline., Conclusions: Progressive and accelerated neurogenic sarcopenia may precede and potentially predict cognitive deficits observed in AD., (© 2024 The Authors. Journal of Cachexia, Sarcopenia and Muscle published by Wiley Periodicals LLC.)

Pathogenic variants in GFPT1, encoding a key enzyme to synthesize UDP-N-acetylglucosamine (UDP-GlcNAc), cause congenital myasthenic syndrome (CMS). We made a knock-in (KI) mouse model carrying a frameshift variant in Gfpt1 exon 9, simulating that found in a patient with CMS. As Gfpt1 exon 9 is exclusively expressed in striated muscles, Gfpt1-KI mice were deficient for Gfpt1 only in skeletal muscles. In Gfpt1-KI mice, (1) UDP-HexNAc, CMP-NeuAc and protein O-GlcNAcylation were reduced in skeletal muscles; (2) aged Gfpt1-KI mice showed poor exercise performance and abnormal neuromuscular junction structures; and (3) markers of the unfolded protein response (UPR) were elevated in skeletal muscles. Denervation-mediated enhancement of endoplasmic reticulum (ER) stress in Gfpt1-KI mice facilitated protein folding, ubiquitin-proteasome degradation and apoptosis, whereas autophagy was not induced and protein aggregates were markedly increased. Lack of autophagy was accounted for by enhanced degradation of FoxO1 by increased Xbp1-s/u proteins. Similarly, in Gfpt1-silenced C2C12 myotubes, ER stress exacerbated protein aggregates and activated apoptosis, but autophagy was attenuated. In both skeletal muscles in Gfpt1-KI mice and Gfpt1-silenced C2C12 myotubes, maladaptive UPR failed to eliminate protein aggregates and provoked apoptosis., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Background: Amyotrophic lateral sclerosis (ALS) is characterized by progressive motor neuron (MN) degeneration, leading to neuromuscular junction (NMJ) dismantling and severe muscle atrophy. The nuclear receptor interaction protein (NRIP) functions as a multifunctional protein. It directly interacts with calmodulin or α-actinin 2, serving as a calcium sensor for muscle contraction and maintaining sarcomere integrity. Additionally, NRIP binds with the acetylcholine receptor (AChR) for NMJ stabilization. Loss of NRIP in muscles results in progressive motor neuron degeneration with abnormal NMJ architecture, resembling ALS phenotypes. Therefore, we hypothesize that NRIP could be a therapeutic factor for ALS., Methods: We used SOD1 G93A mice, expressing human SOD1 with the ALS-linked G93A mutation, as an ALS model. An adeno-associated virus vector encoding the human NRIP gene (AAV-NRIP) was generated and injected into the muscles of SOD1 G93A mice at 60 days of age, before disease onset. Pathological and behavioral changes were measured to evaluate the therapeutic effects of AAV-NRIP on the disease progression of SOD1 G93A mice., Results: SOD1 G93A mice exhibited lower NRIP expression than wild-type mice in both the spinal cord and skeletal muscle tissues. Forced NRIP expression through AAV-NRIP intramuscular injection was observed in skeletal muscles and retrogradely transduced into the spinal cord. AAV-NRIP gene therapy enhanced movement distance and rearing frequencies in SOD1 G93A mice. Moreover, AAV-NRIP increased myofiber size and slow myosin expression, ameliorated NMJ degeneration and axon terminal denervation at NMJ, and increased the number of α-motor neurons (α-MNs) and compound muscle action potential (CMAP) in SOD1 G93A mice., Conclusions: AAV-NRIP gene therapy ameliorates muscle atrophy, motor neuron degeneration, and axon terminal denervation at NMJ, leading to increased NMJ transmission and improved motor functions in SOD1 G93A mice. Collectively, AAV-NRIP could be a potential therapeutic drug for ALS., (© 2024. The Author(s).)

Amyotrophic lateral sclerosis (ALS) is a complex neuromuscular disease characterized by progressive motor neuron degeneration, neuromuscular junction dismantling, and muscle wasting. The pathological and therapeutic studies of ALS have long been neurocentric. However, recent insights have highlighted the significance of peripheral tissue, particularly skeletal muscle, in disease pathology and treatment. This is evidenced by restricted ALS-like muscle atrophy, which can retrogradely induce neuromuscular junction and motor neuron degeneration. Moreover, therapeutics targeting skeletal muscles can effectively decelerate disease progression by modulating muscle satellite cells for muscle repair, suppressing inflammation, and promoting the recovery or regeneration of the neuromuscular junction. This review summarizes and discusses therapeutic strategies targeting skeletal muscles for ALS treatment. It aims to provide a comprehensive reference for the development of novel therapeutics targeting skeletal muscles, potentially ameliorating the progression of ALS.

Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant neurological disorder caused by deleterious CAG repeat expansion in the coding region of the ataxin 7 gene (polyQ-ataxin-7). Infantile-onset SCA7 leads to severe clinical manifestation of respiratory distress, but the exact cause of respiratory impairment remains unclear. Using the infantile-SCA7 mouse model, the SCA7266Q/5Q mouse, we examined the impact of pathological polyQ-ataxin-7 on hypoglossal (XII) and phrenic motor units. We identified the transcript profile of the medulla and cervical spinal cord and investigated the XII and phrenic nerves and the neuromuscular junctions in the diaphragm and tongue. SCA7266Q/5Q astrocytes showed significant intranuclear inclusions of ataxin-7 in the XII and putative phrenic motor nuclei. Transcriptomic analysis revealed dysregulation of genes involved in amino acid and neurotransmitter transport and myelination. Additionally, SCA7266Q/5Q mice demonstrated blunted efferent output of the XII nerve and demyelination in both XII and phrenic nerves. Finally, there was an increased number of neuromuscular junction clusters with higher expression of synaptic markers in SCA7266Q/5Q mice compared with WT controls. These preclinical findings elucidate the underlying pathophysiology responsible for impaired glial cell function and death leading to dysphagia, aspiration, and respiratory failure in infantile SCA7.

Dorsal switch protein 1(DSP1), a mammalian homolog of HMGB1, is firstly identified as a dorsal co-repressor in 1994. DSP1 contains HMG-box domain and functions as a transcriptional regulator in Drosophila melanogaster. It plays a crucial role in embryonic development, particularly in dorsal-ventral patterning during early embryogenesis, through the regulation of gene expression. Moreover, DSP1 is implicated in various cellular processes, including cell fate determination and tissue differentiation, which are essential for embryonic development. While the function of DSP1 in embryonic development has been relatively well-studied, its role in the adult Drosophila brain remains less understood. In this study, we investigated the role of DSP1 in the brain by using neuronal-specific DSP1 overexpression flies. We observed that climbing ability and life span are decreased in DSP1-overexpressed flies. Furthermore, these flies demonstrated neuromuscular junction (NMJ) defect, reduced eye size and a decrease in tyrosine hydroxylase (TH)-positive neurons, indicating neuronal toxicity induced by DSP1 overexpression. Our data suggest that DSP1 overexpression leads to neuronal dysfunction and toxicity, positioning DSP1 as a potential therapeutic target for neurodegenerative diseases., (© 2024. The Author(s).)

5q-Spinal muscular atrophy (5q-SMA) is one of the most common neuromuscular diseases due to homozygous mutations in the SMN1 gene. This leads to a loss of function of the SMN1 gene, which in the end determines lower motor neuron degeneration. Since the generation of the first mouse models of SMA neuropathology, a complex degenerative involvement of the neuromuscular junction and peripheral axons of motor nerves, alongside lower motor neurons, has been described. The involvement of the neuromuscular junction in determining disease symptoms offers a possible parallel therapeutic target. This narrative review aims at providing an overview of the current knowledge about the pathogenesis and significance of neuromuscular junction dysfunction in SMA, circulating biomarkers, outcome measures and available or developing therapeutic approaches.

Purpose: Mitofusin 2 (Mfn2) is one of two mitofusins involved in regulating mitochondrial size, shape and function, including mitophagy, an important cellular mechanism to limit oxidative stress. Reduced expression of Mfn2 has been associated with impaired osteoblast differentiation and function and a reduction in the number of viable osteocytes in bone. We hypothesized that the genetic absence of Mfn2 in these cells would increase their susceptibility to aging-associated metabolic stress, leading to a progressive impairment in skeletal homeostasis over time., Methods: Mfn2 was selectively deleted in vivo at three different stages of osteoblast lineage commitment by crossing mice in which the Mfn2 gene was floxed with transgenic mice expressing Cre under the control of the promoter for Osterix (OSX), collagen1a1, or DMP1 (Dentin Matrix Acidic Phosphoprotein 1)., Results: Mice in which Mfn2 was deleted using DMP1-cre demonstrated a progressive and dramatic decline in bone mineral density (BMD) beginning at 10 weeks of age (n = 5 for each sex and each genotype from age 10 to 20 weeks). By 15 weeks, there was evidence for a functional decline in muscle performance as assessed using a rotarod apparatus (n = 3; 2 males/ 1 female for each genotype), accompanied by a decline in lean body mass. A marked reduction in trabecular bone mass was evident on bone histomorphometry, and biomechanical testing at 25 weeks (k/o: 2 male/1 female, control 2 male/2 female) revealed severely impaired femur strength. Extensive regional myofiber atrophy and degeneration was observed on skeletal muscle histology. Electron microscopy showed progressive disruption of cellular architecture, with disorganized sarcomeres and a bloated mitochondrial reticulum. There was also evidence of neurodegeneration within the ventral horn and roots of the lumbar spinal cord, which was accompanied by myelin loss and myofiber atrophy. Deletion of Mfn2 using OSX-cre or Col1a1-cre did not result in a musculoskeletal phenotype. Where possible, male and female animals were analyzed separately, but small numbers of animals in each group limited statistical power. For other outcomes, where sex was not considered, small sample sizes might still limit the strength of the observation., Conclusion: Despite known functional overlap of Mfn1 and Mfn2 in some tissues, and their co-expression in bone, muscle and spinal cord, deletion of Mfn2 using the 8 kB DMP1 promoter uncovered an important non-redundant role for Mfn2 in maintaining the neuromuscular/bone axis., Competing Interests: Declaration of competing interest None of the authors have any conflicts of interest to disclose., (Copyright © 2024. Published by Elsevier Inc.)

Neuromuscular junction (NMJ) degeneration is one of pathological factors of sarcopenia. Low-magnitude high-frequency vibration (LMHFV) was reported effective in alleviating the sarcopenia progress. However, no previous study has investigated treatment effects of LMHFV targeting NMJ degeneration in sarcopenia. We first compared morphological differences of NMJ between sarcopenic and non-sarcopenic subjects, as well as young and old C57BL/6 mice. We then systematically characterized the age-related degeneration of NMJ in SAMP8 against its control strain, SAMR1 mice, from 3 to 12 months old. We also investigated effects of LMHFV in SAMP8 on the maintenance of NMJ during the onset of sarcopenia with respect to the Agrin-LRP4-MuSK-Dok7 pathway and investigated the mechanism related to ERK1/2 signaling. We observed sarcopenic/old NMJ presented increased acetylcholine receptors (AChRs) cluster fragmentation and discontinuity than non-sarcopenic/young NMJ. In SAMP8, NMJ degeneration (morphologically at 6 months and functionally at 8 months) was observed associated with the sarcopenia onset (10 months). SAMR1 showed improved NMJ morphology and function compared with SAMP8 at 10 months. Skeletal muscle performance was improved at Month 4 post-LMHFV treatment. Vibration group presented improved NMJ function at Months 2 and 6 posttreatment, accompanied with alleviated morphological degeneration at Month 4 posttreatment. LMHFV increased Dok7 expression at Month 4 posttreatment. In vitro, LMHFV could promote AChRs clustering in myotubes by increasing Dok7 expression through suppressing ERK1/2 phosphorylation. In conclusion, NMJ degeneration was observed associated with the sarcopenia onset in SAMP8. LMHFV may attenuate NMJ degeneration and sarcopenia progression by increasing Dok7 expression through suppressing ERK1/2 phosphorylation., (© 2024 The Authors. Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.)

Background: The key pathological signature of ALS/ FTLD is the mis-localization of endogenous TDP-43 from the nucleus to the cytoplasm. However, TDP-43 gain of function in the cytoplasm is still poorly understood since TDP-43 animal models recapitulating mis-localization of endogenous TDP-43 from the nucleus to the cytoplasm are missing., Methods: CRISPR/Cas9 technology was used to generate a zebrafish line (called CytoTDP), that mis-locates endogenous TDP-43 from the nucleus to the cytoplasm. Phenotypic characterization of motor neurons and the neuromuscular junction was performed by immunostaining, microglia were immunohistochemically localized by whole-mount tissue clearing and muscle ultrastructure was analyzed by scanning electron microscopy. Behavior was investigated by video tracking and quantitative analysis of swimming parameters. RNA sequencing was used to identify mis-regulated pathways with validation by molecular analysis., Results: CytoTDP fish have early larval phenotypes resembling clinical features of ALS such as progressive motor defects, neurodegeneration and muscle atrophy. Taking advantage of zebrafish's embryonic development that solely relys on yolk usage until 5 days post fertilization, we demonstrated that microglia proliferation and activation in the hypothalamus is independent from food intake. By comparing CytoTDP to a previously generated TDP-43 knockout line, transcriptomic analyses revealed that mis-localization of endogenous TDP-43, rather than TDP-43 nuclear loss of function, leads to early onset metabolic dysfunction., Conclusions: The new TDP-43 model mimics the ALS/FTLD hallmark of progressive motor dysfunction. Our results suggest that functional deficits of the hypothalamus, the metabolic regulatory center, might be the primary cause of weight loss in ALS patients. Cytoplasmic gain of function of endogenous TDP-43 leads to metabolic dysfunction in vivo that are reminiscent of early ALS clinical non-motor metabolic alterations. Thus, the CytoTDP zebrafish model offers a unique opportunity to identify mis-regulated targets for therapeutic intervention early in disease progression., (© 2024. The Author(s).)

Loss-of-function mutations in MEGF10 lead to a rare and understudied neuromuscular disorder known as MEGF10-related myopathy. There are no treatments for the progressive respiratory distress, motor impairment, and structural abnormalities in muscles caused by the loss of MEGF10 function. In this study, we deployed cellular and molecular assays to obtain additional insights about MEGF10-related myopathy in juvenile, young adult, and middle-aged Megf10 knockout (KO) mice. We found fewer muscle fibers in juvenile and adult Megf10 KO mice, supporting published studies that MEGF10 regulates myogenesis by affecting satellite cell differentiation. Interestingly, muscle fibers do not exhibit morphological hallmarks of atrophy in either young adult or middle-aged Megf10 KO mice. We next examined the neuromuscular junction (NMJ), in which MEGF10 has been shown to concentrate postnatally, using light and electron microscopy. We found early and progressive degenerative features at the NMJs of Megf10 KO mice that include increased postsynaptic fragmentation and presynaptic regions not apposed by postsynaptic nicotinic acetylcholine receptors. We also found perisynaptic Schwann cells intruding into the NMJ synaptic cleft. These findings strongly suggest that the NMJ is a site of postnatal pathology in MEGF10-related myopathy. In support of these cellular observations, RNA-seq analysis revealed genes and pathways associated with myogenesis, skeletal muscle health, and NMJ stability dysregulated in Megf10 KO mice compared to wild-type mice. Altogether, these data provide new and valuable cellular and molecular insights into MEGF10-related myopathy., (© 2024. The Author(s).)

The primary neural circuit affected in Amyotrophic Lateral Sclerosis (ALS) patients is the corticospinal motor circuit, originating in upper motor neurons (UMNs) in the cerebral motor cortex which descend to synapse with the lower motor neurons (LMNs) in the spinal cord to ultimately innervate the skeletal muscle. Perturbation of these neural circuits and consequent loss of both UMNs and LMNs, leading to muscle wastage and impaired movement, is the key pathophysiology observed. Despite decades of research, we are still lacking in ALS disease-modifying treatments. In this review, we document the current research from patient studies, rodent models, and human stem cell models in understanding the mechanisms of corticomotor circuit dysfunction and its implication in ALS. We summarize the current knowledge about cortical UMN dysfunction and degeneration, altered excitability in LMNs, neuromuscular junction degeneration, and the non-cell autonomous role of glial cells in motor circuit dysfunction in relation to ALS. We further highlight the advances in human stem cell technology to model the complex neural circuitry and how these can aid in future studies to better understand the mechanisms of neural circuit dysfunction underpinning ALS.

Skeletal muscle is characterized by a remarkable capacity to rearrange after physiological changes and efficiently regenerate. However, during aging, extensive injury, or pathological conditions, the complete regenerative program is severely affected, with a progressive loss of muscle mass and function, a condition known as sarcopenia. The compromised tissue repair program is attributable to the gradual depletion of stem cells and to altered regulatory signals. Defective muscle regeneration can severely affect re-innervation by motor axons, and neuromuscular junctions (NMJs) development, ultimately leading to skeletal muscle atrophy. Defects in NMJ formation and maintenance occur physiologically during aging and are responsible for the pathogenesis of several neuromuscular disorders. However, it is still largely unknown how neuromuscular connections are restored on regenerating fibers. It has been suggested that attractive and repelling signals used for axon guidance could be implicated in this process; in particular, guidance molecules called semaphorins play a key role. Semaphorins are a wide family of extracellular regulatory signals with a multifaceted role in cell-cell communication. Originally discovered as axon guidance factors, they have been implicated in cancer progression, embryonal organogenesis, skeletal muscle innervation, and other physiological and developmental functions in different tissues. In particular, in skeletal muscle, specific semaphorin molecules are involved in the restoration and remodeling of the nerve-muscle connections, thus emphasizing their plausible role to ensure the success of muscle regeneration. This review article aims to discuss the impact of aging on skeletal muscle regeneration and NMJs remodeling and will highlight the most recent insights about the role of semaphorins in this context.

Myasthenia gravis (MG) stands as a perplexing autoimmune disorder affecting the neuromuscular junction, driven by a multitude of antibodies targeting postsynaptic elements. However, the mystery of MG pathogenesis has yet to be completely uncovered, and its heterogeneity also challenges diagnosis and treatment. Growing evidence shows the differential expression of non-coding RNAs (ncRNAs) in MG has played an essential role in the development of MG in recent years. Remarkably, these aberrantly expressed ncRNAs exhibit distinct profiles within diverse clinical subgroups and among patients harboring various antibody types. Furthermore, they have been implicated in orchestrating the production of inflammatory cytokines, perturbing the equilibrium of T helper 1 cells (Th1), T helper 17 cells (Th17), and regulatory T cells (Tregs), and inciting B cells to generate antibodies. Studies have elucidated that certain ncRNAs mirror the clinical severity of MG, while others may hold therapeutic significance, showcasing a propensity to return to normal levels following appropriate treatments or potentially foretelling the responsiveness to immunosuppressive therapies. Notably, the intricate interplay among these ncRNAs does not follow a linear trajectory but rather assembles into a complex network, with competing endogenous RNA (ceRNA) emerging as a prominent hub in some cases. This comprehensive review consolidates the landscape of dysregulated ncRNAs in MG, briefly delineating their pivotal role in MG pathogenesis. Furthermore, it explores their promise as prospective biomarkers, aiding in the elucidation of disease subtypes, assessment of disease severity, monitoring therapeutic responses, and as novel therapeutic targets., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Wang, Zhu, Liu, Hu and Zhu.)

Myasthenia gravis (MG) is a prototypical autoimmune disease of the neuromuscular junction (NMJ). The study of the underlying pathophysiology has provided novel insights into the interplay of autoantibodies and complement-mediated tissue damage. Experimental autoimmune myasthenia gravis (EAMG) emerged as a valuable animal model, designed to gain further insight and to test novel therapeutic approaches for MG. However, the availability of native acetylcholine receptor (AChR) protein is limited favouring the use of recombinant proteins. To provide a simplified platform for the study of MG, we established a model of EAMG using a recombinant protein containing the immunogenic sequence of AChR in mice. This model recapitulates key features of EAMG, including fatigable muscle weakness, the presence of anti-AChR-antibodies, and engagement of the NMJ by complement and a reduced NMJ density. Further characterization of this model demonstrated a prominent B cell immunopathology supported by T follicular helper cells. Taken together, the herein-presented EAMG model may be a valuable tool for the study of MG pathophysiology and the pre-clinical testing of therapeutic applications.

PDZ domain-containing RING finger family protein 3 (PDZRN3) is expressed in various tissues, including the skeletal muscle. Although PDZRN3 plays a crucial role in the terminal differentiation of myoblasts and synaptic growth/maturation in myogenesis, the role of this molecule in postnatal muscles is completely unknown despite its lifelong expression in myofibers. In this study, we aimed to elucidate the function of PDZRN3 in mature myofibers using myofiber-specific conditional knockout mice. After tamoxifen injection, PDZRN3 deficiency was confirmed in both fast and slow myofibers of Myf6-CreER T2 ; Pdzrn3 flox/flox (Pdzrn3 mcKO ) mice. Transcriptome analysis of the skeletal muscles of Pdzrn3 mcKO mice identified differentially expressed genes, including muscle atrophy-related genes such as Smox, Amd1/2, and Mt1/2, suggesting that PDZRN3 is involved in the homeostatic maintenance of postnatal muscles. PDZRN3 deficiency caused muscle atrophy, predominantly in fast-twitch (type II) myofibers, and reduced muscle strength. While myofiber-specific PDZRN3 deficiency did not influence endplate morphology or expression of neuromuscular synaptic formation-related genes in postnatal muscles, indicating that the relationship between PDZRN3 and neuromuscular junctions might be limited during muscle development. Considering that the expression of Pdzrn3 in skeletal muscles was significantly lower in aged mice than in mature adult mice, we speculated that the PDZRN3-mediated muscle maintenance system might be associated with the pathophysiology of age-related muscle decline, such as sarcopenia., Competing Interests: Declaration of competing interest The authors declare that they have no competing financial interests related to personal relationships that could have influenced the work reported in this study., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

The complex neuromuscular network that controls body movements is the target of severe diseases that result in paralysis and death. Here, we report the development of a robust and efficient self-organizing neuromuscular junction (soNMJ) model from human pluripotent stem cells that can be maintained long-term in simple adherent conditions. The timely application of specific patterning signals instructs the simultaneous development and differentiation of position-specific brachial spinal neurons, skeletal muscles, and terminal Schwann cells. High-content imaging reveals self-organized bundles of aligned muscle fibers surrounded by innervating motor neurons that form functional neuromuscular junctions. Optogenetic activation and pharmacological interventions show that the spinal neurons actively instruct the synchronous skeletal muscle contraction. The generation of a soNMJ model from spinal muscular atrophy patient-specific iPSCs reveals that the number of NMJs and muscle contraction is severely affected, resembling the patient's pathology. In the future, the soNMJ model could be used for high-throughput studies in disease modeling and drug development. Thus, this model will allow us to address unmet needs in the neuromuscular disease field., (© 2023. The Author(s).)

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., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Guarantors of Brain.)

Myasthenia gravis is an autoimmune disease caused by the presence of specific antibodies targeting different postsynaptic components of the neuromuscular junction, and is clinically characterized by the presence of fatigueable muscle weakness. In the etiopathogenesis plays a central role the thymus and the most frequently detected pathogenic autoantibodies are targeted to the acetylcholine receptor. The increase in the knowledge of the immunological components of the neuromuscular junction in the last two decades has been fundamental to identify new pathogenic antibodies, reduce the percentage of patients with seronegative myasthenia, and propose a classification of patients into subgroups with clinical-therapeutic interest. In addition, in recent years, new drugs have been developed for the treatment of patients with myasthenia gravis that are refractory to conventional immunosuppressive treatment., (Copyright © 2023 Elsevier España, S.L.U. All rights reserved.)

Sarcopenia, or age-related decline in muscle form and function, exerts high personal, societal, and economic burdens when untreated. Integrity and function of the neuromuscular junction (NMJ), as the nexus between the nervous and muscular systems, is critical for input and dependable neural control of muscle force generation. As such, the NMJ has long been a site of keen interest in the context of skeletal muscle function deficits during aging and in the context of sarcopenia. Historically, changes of NMJ morphology during aging have been investigated extensively but primarily in aged rodent models. Aged rodents have consistently shown features of NMJ endplate fragmentation and denervation. Yet, the presence of NMJ changes in older humans remains controversial, and conflicting findings have been reported. This review article describes the physiological processes involved in NMJ transmission, discusses the evidence that supports NMJ transmission failure as a possible contributor to sarcopenia, and speculates on the potential of targeting these defects for therapeutic development. The technical approaches that are available for assessment of NMJ transmission, whether each approach has been applied in the context of aging and sarcopenia, and the associated findings are summarized. Like morphological studies, age-related NMJ transmission deficits have primarily been studied in rodents. In preclinical studies, isolated synaptic electrophysiology recordings of endplate currents or potentials have been mostly used, and paradoxically, have shown enhancement, rather than failure, with aging. Yet, in vivo assessment of single muscle fiber action potential generation using single fiber electromyography and nerve-stimulated muscle force measurements show evidence of NMJ failure in aged mice and rats. Together these findings suggest that endplate response enhancement may be a compensatory response to post-synaptic mechanisms of NMJ transmission failure in aged rodents. Possible, but underexplored, mechanisms of this failure are discussed including the simplification of post-synaptic folding and altered voltage-gated sodium channel clustering or function. In humans, there is limited clinical data that has selectively investigated single synaptic function in the context of aging. If sarcopenic older adults turn out to exhibit notable impairments in NMJ transmission (this has yet to be examined but based on available evidence appears to be plausible) then these NMJ transmission defects present a well-defined biological mechanism and offer a well-defined pathway for clinical implementation. Investigation of small molecules that are currently available clinically or being testing clinically in other disorders may provide a rapid route for development of interventions for older adults impacted by sarcopenia., Competing Interests: Declaration of Competing Interest In the past 5 years, W. David Arnold has received research funding from NIH, NMD Pharma, and Avidity Biosciences. In the past 5 years, W. David Arnold has received consulting fees from Amplo Biosciences, NMD Pharma, Avidity Biosciences, Dyne Therapeutics, Novartis, La Hoffmann Roche, Genentech, Design Therapeutics, Cadent Therapeutics, and Catalyst Pharmaceuticals. In the past 5 years, Brian Clark has received research funding from the NIH, NMD Pharma, Astellas Pharma Global Development, Inc., and RTI Health Solutions for contracted studies that involved aging and muscle related research. In the past 5-years, Brian Clark has received consulting fees from Regeneron Pharmaceuticals and the Gerson Lehrman Group for consultation specific to age-related muscle weakness. Brian Clark is a co-founder with equity of OsteoDx Inc., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Aims: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with complex aetiology. Despite evidence of neuromuscular junction (NMJ) denervation and 'dying-back' pathology in models of SOD1-dependent ALS, evidence in other genetic forms of ALS is limited by a lack of suitable animal models. TDP-43, a key mediator protein in ALS, is overexpressed in neurons in Thy1-hTDP-43 WT mice. We therefore aimed to comprehensively analyse NMJ pathology in this model of ALS., Methods: Expression of TDP-43 was assessed via western blotting. Immunohistochemistry techniques, alongside NMJ-morph quantification, were used to analyse motor neuron number, NMJ denervation status and terminal Schwann cell morphology., Results: We present a time course of progressive, region-specific motor neuron pathology in Thy1-hTDP-43 WT mice. Thy1-driven hTDP-43 expression increased steadily, correlating with developing hindlimb motor weakness and associated motor neuron loss in the spinal cord with a median survival of 21 days. Pronounced NMJ denervation was observed in hindlimb muscles, mild denervation in cranial muscles but no evidence of denervation in either forelimb or trunk muscles. NMJ pathology was restricted to motor nerve terminals, with denervation following the same time course as motor neuron loss. Terminal Schwann cells were lost from NMJs in hindlimb muscles, directly correlating with denervation status., Conclusions: Thy1-hTDP-43 WT mice represent a severe model of ALS, with NMJ pathology/denervation of distal muscles and motor neuron loss, as observed in ALS patients. This model therefore provides an ideal platform to investigate mechanisms of dying-back pathology, as well as NMJ-targeting disease-modifying therapies in ALS., (© 2023 The Authors. Neuropathology and Applied Neurobiology published by John Wiley & Sons Ltd on behalf of British Neuropathological Society.)

Duchenne muscular dystrophy (DMD) is a severe, progressive, muscle-wasting disease, characterized by progressive deterioration of skeletal muscle that causes rapid loss of mobility. The failure in respiratory and cardiac muscles is the underlying cause of premature death in most patients with DMD. Mutations in the gene encoding dystrophin result in dystrophin deficiency, which is the underlying pathogenesis of DMD. Dystrophin-deficient myocytes are dysfunctional and vulnerable to injury, triggering a series of subsequent pathological changes. In this review, we detail the molecular mechanism of DMD, dystrophin deficiency-induced muscle cell damage (oxidative stress injury, dysregulated calcium homeostasis, and sarcolemma instability) and other cell damage and dysfunction (neuromuscular junction impairment and abnormal differentiation of muscle satellite). We also describe aberrant function of other cells and impaired muscle regeneration due to deterioration of the muscle microenvironment, and dystrophin deficiency-induced multiple organ dysfunction, while summarizing the recent advances in the treatment of DMD., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany.)

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.

Objectives: Inherited defects of the neuromuscular junction (NMJ) comprise an increasingly diverse range of diseases. Several recently identified genes highlight the overlap between peripheral neuropathies and congenital myasthenic syndromes (CMS). The beta-2 adrenergic receptor agonist salbutamol has been shown to provide symptomatic benefit in CMS, while improving structural defects at the NMJ. Based on these findings, we identified cases of motor neuropathy with NMJ dysfunction and assessed the effect of salbutamol on motor function., Methods: Cases of motor neuropathy with significant NMJ dysfunction, were identified using repetitive nerve stimulation and single fibre electromyography. Oral salbutamol was administered for 12 months. Repeat neurophysiological and clinical assessments were undertaken at baseline, 6 months and 12 months., Results: Significant defects of neuromuscular transmission were identified in 15 patients harbouring a range of genetic defects, including mutations in GARS1, DNM2, SYT2 and DYNC1H. No clear benefit on motor function was seen following the administration of 12 months of oral salbutamol; however, there was a significant improvement in patient reported fatigue. In addition, no clear effect on neurophysiological parameters was seen in patients treated with salbutamol. Side-effects due to off-target beta-adrenergic effects were significant in the patient cohort., Conclusion: These results highlight the involvement of the NMJ in several subtypes of motor neuropathies, including subtypes of neuropathy due to deficits in mitochondrial fusion-fission, synaptic vesicle transport, calcium channels and tRNA synthetases. Whether the NMJ dysfunction is simply due to muscle reinnervation or a pathology unrelated to denervation is unknown. The involvement of the NMJ may represent a novel therapeutic target in these conditions. However, treatment regimens will need to be more targeted for patients with primary inherited defects of neuromuscular transmission., (© 2023. The Author(s).)

Neuromuscular junctions (NMJs) are specialized synapses, crucial for the communication between spinal motor neurons (MNs) and skeletal muscle. NMJs become vulnerable in degenerative diseases, such as muscle atrophy, where the crosstalk between the different cell populations fails, and the regenerative ability of the entire tissue is hampered. How skeletal muscle sends retrograde signals to MNs through NMJs represents an intriguing field of research, and the role of oxidative stress and its sources remain poorly understood. Recent works demonstrate the myofiber regeneration potential of stem cells, including amniotic fluid stem cells (AFSC), and secreted extracellular vesicles (EVs) as cell-free therapy. To study NMJ perturbations during muscle atrophy, we generated an MN/myotube co-culture system through Xona TM microfluidic devices, and muscle atrophy was induced in vitro by Dexamethasone (Dexa). After atrophy induction, we treated muscle and MN compartments with AFSC-derived EVs (AFSC-EVs) to investigate their regenerative and anti-oxidative potential in counteracting NMJ alterations. We found that the presence of EVs reduced morphological and functional in vitro defects induced by Dexa. Interestingly, oxidative stress, occurring in atrophic myotubes and thus involving neurites as well, was prevented by EV treatment. Here, we provided and validated a fluidically isolated system represented by microfluidic devices for studying human MN and myotube interactions in healthy and Dexa-induced atrophic conditions-allowing the isolation of subcellular compartments for region-specific analyses-and demonstrated the efficacy of AFSC-EVs in counteracting NMJ perturbations.