Mutations in the FUS/TLS gene on chromosome 16 cause familial amyotrophic lateral sclerosis

ATXN2L primarily interacts with NUFIP2, the absence of ATXN2L results in NUFIP2 depletion, and the ATXN2-polyQ expansion triggers NUFIP2 accumulation

The cytoplasmic Ataxin-2 (ATXN2) protein associates with TDP-43 in stress granules (SG) where RNA quality control occurs. Mutations in this pathway underlie Spinocerebellar Ataxia type 2 (SCA2) and Amyotrophic Lateral Sclerosis. In contrast, Ataxin-2-like (ATXN2L) is predominantly perinuclear, more abundant, and essential for embryonic life. Its sequestration into ATXN2 aggregates may contribute to disease. In this study, we utilized two approaches to clarify the roles of ATXN2L. First, we identified interactors through co-immunoprecipitation in both wild-type and ATXN2L-null murine embryonic fibroblasts. Second, we assessed the proteome profile effects using mass spectrometry in these cells. Additionally, we examined the accumulation of ATXN2L interactors in the SCA2 mouse model, Atxn2-CAG100-KnockIn (KIN). We observed that RNA-binding proteins, including PABPN1, NUFIP2, MCRIP2, RBMS1, LARP1, PTBP1, FMR1, RPS20, FUBP3, MBNL2, ZMAT3, SFPQ, CSDE1, HNRNPK, and HNRNPDL, exhibit a stronger association with ATXN2L compared to established interactors like ATXN2, PABPC1, LSM12, and G3BP2. Additionally, ATXN2L interacted with components of the actin complex, such as SYNE2, LMOD1, ACTA2, FYB, and GOLGA3. We noted that oxidative stress increased HNRNPK but decreased SYNE2 association, which likely reflects the relocalization of SG. Proteome profiling revealed that NUFIP2 and SYNE2 are depleted in ATXN2L-null fibroblasts. Furthermore, NUFIP2 homodimers and SYNE1 accumulate during the ATXN2 aggregation process in KIN 14-month-old spinal cord tissues. The functions of ATXN2L and its interactors are therefore critical in RNA granule trafficking and surveillance, particularly for the maintenance of differentiated neurons.

Protein Structure-based FUS Mutational Subtypes Are Associated With Protein Mislocalization in Amyotrophic Lateral Sclerosis Patients

The mislocalization of RNA-binding proteins (RBPs) from nucleus to cytoplasm and the formation of aggregates are hallmarks of neurodegeneration. Amyotrophic lateral sclerosis (ALS) disease-causing mutations in the fused in sarcoma (FUS) gene, encoding an RNA-binding protein, cluster at the C-terminal proline/tyrosine-nuclear localization signal (PY-NLS) domain, which is crucial for mediating nucleus-cytoplasm translocation by binding to Transportin-1. However, the mechanisms underlying heterogeneous protein mislocalization and age at onset (AAO) of ALS cases carrying FUS PY-NLS mutations remain unclear. Here, we screened FUS mutations in 416 ALS patients, and identified 12 patients carrying four FUS mutations at the p.R521 locus of PY-NLS domain (p.R521P, p.R521C, p.R521G, p.R521H), exhibiting highly variable AAO (20-56 years). AlphaFold-2 predicted protein structures classified FUS p.R521 mutants into alpha-helix containing (p.R521C, p.R521H) and alpha-helix disrupted (p.R521P, p.R521G) subgroups. Isothermal titration calorimetry experiment showed that the FUS alpha-helix disrupted subgroup had a reduced binding affinity with transportin-1, which is essential for mediating the nucleus-cytoplasm translocation. Furthermore, immunofluorescence in HEK-293 T and SH-SY5Y cells revealed more protein mislocalization in the FUS alpha-helix disrupted subgroup compared to the alpha-helix containing subgroup. FUS mislocalization status is also significantly associated with ALS AAO. Finally, the alpha-helix structure based FUS-ALS subgroups exhibited significantly different AAO (P = 0.036) in our cohort, but not in a Chinese cohort including published dataset. In summary, we showed highly diverse phenotypes in ALS patients with FUS R521 mutants, and implicated a link between genetic mutation related C-terminal structure with the status of FUS protein mislocalization.

Seeded aggregation of TDP-43 induces its loss of function and reveals early pathological signatures

Neurodegeneration in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) results from both gain of toxicity and loss of normal function of the RNA-binding protein TDP-43, but their mechanistic connection remains unclear. Increasing evidence suggests that TDP-43 aggregates act as self-templating seeds, propagating pathology through the central nervous system via a prion-like cascade. We developed a robust TDP-43-seeding platform for quantitative assessment of TDP-43 aggregate uptake, cell-to-cell spreading, and loss of function within living cells, while they progress toward pathology. We show that both patient-derived and recombinant TDP-43 pathological aggregates were abundantly internalized by human neuron-like cells, efficiently recruited endogenous TDP-43, and formed cytoplasmic inclusions reminiscent of ALS/FTD pathology. Combining a fluorescent reporter of TDP-43 function with RNA sequencing and proteomics, we demonstrated aberrant cryptic splicing and a loss-of-function profile resulting from TDP-43-templated aggregation. Our data highlight known and novel pathological signatures in the context of seed-induced TDP-43 loss of function.

Genetic Basis of Motor Neuron Diseases: Insights, Clinical Management, and Future Directions

Motor neuron diseases (MNDs) are a heterogeneous group of neurodegenerative disorders characterized by the progressive loss of motor neurons, resulting in debilitating physical decline. Advances in genetics have revolutionized the understanding of MNDs, elucidating critical genes such as SOD1, TARDBP, FUS, and C9orf72, which are implicated in their pathogenesis. Despite these breakthroughs, significant gaps persist in understanding the interplay between genetic and environmental factors, the role of rare variants, and epigenetic contributions. This review synthesizes current knowledge on the genetic landscape of MNDs, highlights challenges in linking genotype to phenotype, and discusses the promise of precision medicine approaches. Emphasis is placed on emerging strategies, such as gene therapy and targeted molecular interventions, offering hope for personalized treatments. Addressing these challenges is imperative to harness the full potential of genomics for improving outcomes in MNDs.

Small-molecule dissolution of stress granules by redox modulation benefits ALS models

Neurodegenerative diseases, such as amyotrophic lateral sclerosis, are often associated with mutations in stress granule proteins. Aberrant stress granule condensate formation is associated with disease, making it a potential target for pharmacological intervention. Here, we identified lipoamide, a small molecule that specifically prevents cytoplasmic condensation of stress granule proteins. Thermal proteome profiling showed that lipoamide stabilizes intrinsically disordered domain-containing proteins, including SRSF1 and SFPQ, which are stress granule proteins necessary for lipoamide activity. SFPQ has redox-state-specific condensate dissolving behavior, which is modulated by the redox-active lipoamide dithiolane ring. In animals, lipoamide ameliorates aging-associated aggregation of a stress granule reporter protein, improves neuronal morphology and recovers motor defects caused by amyotrophic lateral sclerosis-associated FUS and TDP-43 mutants. Thus, lipoamide is a well-tolerated small-molecule modulator of stress granule condensation, and dissection of its molecular mechanism identified a cellular pathway for redox regulation of stress granule formation.

Exploring Exosome-Based Approaches for Early Diagnosis and Treatment of Neurodegenerative Diseases

Neurodegenerative diseases (NDs), like Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and Amyotrophic Lateral Sclerosis (ALS), present an increasingly significant global health burden, primarily due to the lack of effective early diagnostic tools and treatments. Exosomes-nano-sized extracellular vesicles secreted by nearly all cell types-have emerged as promising candidates for both biomarkers and therapeutic agents in NDs. This review examines the biogenesis, molecular composition, and diverse functions of exosomes in NDs. Exosomes play a crucial role in mediating intercellular communication. They are capable of reflecting the biochemical state of their parent cells and have the ability to cross the blood-brain barrier (BBB). In doing so, they facilitate the propagation of pathological proteins, such as amyloid-beta (Aβ), tau, and alpha-synuclein (α-syn), while also enabling the targeted delivery of neuroprotective compounds. Recent advancements in exosome isolation and engineering have opened up new possibilities for diagnostic and therapeutic strategies. These range from the discovery of non-invasive biomarkers to innovative approaches in gene therapy and drug delivery systems. However, challenges related to standardization, safety, and long-term effects must be addressed before exosomes can be translated into clinical applications. This review highlights both the promising potential and the obstacles that must be overcome to leverage exosomes in the treatment of NDs and the transformation of personalized medicine.

RNAi-mediated silencing of SOD1 profoundly extends survival and functional outcomes in ALS mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition, with 20% of familial and 2%-3% of sporadic cases linked to mutations in the cytosolic superoxide dismutase (SOD1) gene. Mutant SOD1 protein is toxic to motor neurons, making SOD1 gene suppression a promising approach, supported by preclinical data and the 2023 Federal Drug Administration (FDA) approval of the GapmeR ASO targeting SOD1, tofersen. Despite the approval of an ASO and the optimism it brings to the field, the pharmacodynamics and pharmacokinetics of therapeutic SOD1 modulation can be improved. Here, we developed a chemically stabilized divalent siRNA scaffold (di-siRNA) that effectively suppresses SOD1 expression in vitro and in vivo. With optimized chemical modification, it achieves remarkable CNS tissue permeation and SOD1 silencing in vivo. Administered intraventricularly, di-siRNASOD1 extended survival in SOD1-G93A ALS mice, increasing survival beyond that previously seen in these mice by ASO modalities, slowed disease progression according to the standard ALS preclinical endpoints, and attenuated ALS neuropathology. These properties offer an improved therapeutic strategy for SOD1-mediated ALS and may extend to other dominantly inherited neurological disorders.

Synaptic defects in adult drosophila motor neurons in a model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that primarily affects motor neurons in the brain and spinal cord. Like other neurodegenerative diseases, defects in synaptic integrity are among the earliest hallmarks of ALS. However, the specific impairments to synaptic integrity remain unclear. To better understand synaptic defects in ALS, we expressed either wild-type or mutant Fused in Sarcoma (FUS), an RNA binding protein that is often mis-localized in ALS, in adult motor neurons. Using optogenetic stimulation of the motor neurons innervating the Ventral Abdominal Muscles (VAMs), we found that expression of mutant FUS disrupted the functional integrity of these synapses. This functional deficit was followed by disruption of synaptic gross morphology, localization of pre- and post-synaptic proteins, and cytoskeleton integrity. We found similar synaptic defects using the motor neurons innervating the Dorsal Longitudinal Muscles (DLMs), where expression of mutant FUS resulted in a progressive loss of flight ability along with disruption of active zone distribution. Our findings uncover defects in synaptic function that precede changes in synaptic structure, suggesting that synaptic function is more sensitive to this ALS model. Highlighting the earliest synaptic defects in this disease model should help to identify strategies for preventing later stages of disease progression.

Role and Potential of Artificial Intelligence in Biomarker Discovery and Development of Treatment Strategies for Amyotrophic Lateral Sclerosis

Neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), present significant challenges owing to their complex pathologies and a lack of curative treatments. Early detection and reliable biomarkers are critical but remain elusive. Artificial intelligence (AI) has emerged as a transformative tool, enabling advancements in biomarker discovery, diagnostic accuracy, and therapeutic development. From optimizing clinical-trial designs to leveraging omics and neuroimaging data, AI facilitates understanding of disease and treatment innovation. Notably, technologies such as AlphaFold and deep learning models have revolutionized proteomics and neuroimaging, offering unprecedented insights into ALS pathophysiology. This review highlights the intersection of AI and ALS, exploring the current state of progress and future therapeutic prospects.

TDP-43 seeding activity in the olfactory mucosa of patients with amyotrophic lateral sclerosis

BACKGROUND

In recent years, the seed amplification assay (SAA) has enabled the identification of pathological TDP-43 in the cerebrospinal fluid (CSF) and olfactory mucosa (OM) of patients with genetic forms of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Here, we investigated the seeding activity of TDP-43 in OM samples collected from patients with sporadic ALS.

METHODS

OM samples were collected from patients with (a) sporadic motor neuron diseases (MND), including spinal ALS (n = 35), bulbar ALS (n = 18), primary lateral sclerosis (n = 10), and facial onset sensory and motor neuronopathy (n = 2); (b) genetic MND, including carriers of C9orf72exp (n = 6), TARDBP (n = 4), SQSTM1 (n = 3), C9orf72exp + SQSTM1 (n = 1), OPTN (n = 1), GLE1 (n = 1), FUS (n = 1) and SOD1 (n = 4) mutations; (c) other neurodegenerative disorders (OND), including Alzheimer's disease (n = 3), dementia with Lewy bodies (n = 8) and multiple system atrophy (n = 6); and (d) control subjects (n = 22). All samples were subjected to SAA analysis for TDP-43 (TDP-43_SAA). Plasmatic levels of TDP-43 and neurofilament-light chain (NfL) were also assessed in a selected number of patients.

RESULTS

TDP-43_SAA was positive in 29/65 patients with sporadic MND, 9/21 patients with genetic MND, 6/17 OND patients and 3/22 controls. Surprisingly, one presymptomatic individual also tested positive. As expected, OM of genetic non-TDP-43-related MND tested negative. Interestingly, fluorescence values from non-MND samples that tested positive were consistently and significantly lower than those obtained with sporadic and genetic MND. Furthermore, among TDP-43-positive samples, the lag phase observed in MND patients was significantly longer than that in non-MND patients. Plasma TDP-43 levels were significantly higher in sporadic MND patients compared to controls and decreased as the disease progressed. Similarly, plasma NfL levels were higher in both sporadic and genetic MND patients and positively correlated with disease progression rate (ΔFS). No significant correlations were detected between TDP-43_SAA findings and the biological, clinical, or neuropsychological parameters considered.

CONCLUSIONS

The OM of a subset of patients with sporadic MND can trigger seeding activity for TDP-43, as previously observed in genetic MND. Thus, TDP-43_SAA analysis of OM can improve the clinical characterization of ALS across different phenotypes and enhance our understanding of these diseases. Finally, plasma TDP-43 could serve as a potential biomarker for monitoring disease progression. However, further research is needed to confirm and expand these findings.

Probing the Formation and Liquid-to-Solid Transition of FUS Condensates via the Lifetimes of Fluorescent Proteins

Liquid-liquid phase separation (LLPS) of biomolecules is a fundamental cellular process that is essential for maintaining homeostasis and facilitating biochemical activities. On the other hand, aberrant phase separation alters condensate fluidity and causes a transition from liquid-like condensates to solid-like condensates, which may lead to the formation of the pathological aggregations often observed in neurodegenerative diseases. Condensate fluidity is usually assessed by the fluorescence recovery after photobleaching. Here, we reveal that the fluorescence lifetimes of several fluorescent proteins are sensitive to LLPS and the liquid-to-solid transition. Furthermore, we identify several key residues that regulate the sensitivity of fluorescence lifetimes toward phase separation. Thus, we apply fluorescence lifetime imaging microscopy (FLIM) to visualize LLPS and the liquid-to-solid transition in living cells, demonstrating that FLIM is a nondestructive method for tracking changes in condensate fluidity in real time.

Nanoscale domains govern local diffusion and aging within FUS condensates

Biomolecular condensates regulate cellular physiology by sequestering and processing RNAs and proteins, yet how these processes are locally tuned within condensates remains unclear. Moreover, in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), condensates undergo liquid-to-solid phase transitions, but capturing early intermediates in this process has been challenging. Here, we present a surface multi-tethering approach to achieve intra-condensate single-molecule tracking of fluorescently labeled RNA and protein molecules within liquid-like condensates. Using RNA-binding protein Fused in Sarcoma (FUS) as a model for condensates implicated in ALS, we discover that RNA and protein diffusion is confined within distinct nanometer-scale domains, or nanodomains, which exhibit unique connectivity and chemical environments. During condensate aging, these nanodomains reposition, facilitating FUS fibrilization at the condensate surface, a transition enhanced by FDA-approved ALS drugs. Our findings demonstrate that nanodomain formation governs condensate function by modulating biomolecule sequestration and percolation, offering insights into condensate aging and disease-related transitions.

Drug repurposing in amyotrophic lateral sclerosis (ALS)

INTRODUCTION

Identifying treatments that can alter the natural history of amyotrophic lateral sclerosis (ALS) is challenging. For years, drug discovery in ALS has relied upon traditional approaches with limited success. Drug repurposing, where clinically approved drugs are reevaluated for other indications, offers an alternative strategy that overcomes some of the challenges associated with de novo drug discovery.

AREAS COVERED

In this review, the authors discuss the challenge of drug discovery in ALS and examine the potential of drug repurposing for the identification of new effective treatments. The authors consider a range of approaches, from screening in experimental models to computational approaches, and outline some general principles for preclinical and clinical research to help bridge the translational gap. Literature was reviewed from original publications, press releases and clinical trials.

EXPERT OPINION

Despite remaining challenges, drug repurposing offers the opportunity to improve therapeutic options for ALS patients. Nevertheless, stringent preclinical research will be necessary to identify the most promising compounds together with innovative experimental medicine studies to bridge the translational gap. The authors further highlight the importance of combining expertise across academia, industry and wider stakeholders, which will be key in the successful delivery of repurposed therapies to the clinic.

Release of FUS into the extracellular space is regulated by its amino-terminal prion-like domain

Fused in sarcoma (FUS) is a causative factor of amyotrophic lateral sclerosis (ALS) and is believed to propagate pathologically by transmission from cell to cell. However, the mechanism underlying FUS release from cells, which is a critical step for the propagation system, remains poorly understood. This study conducted an analysis of the release of human and mouse FUS from neurons, revealing that human FUS is significantly released into the media compared to its mouse counterpart. Further study using chimeric FUS proteins identified the amino-terminal region of human FUS as essential for its release. These findings indicate that human FUS is released directly from neurons and underscore the novel functional role of its amino-terminal region in this process.

Genetic risk for neurodegenerative conditions is linked to disease-specific microglial pathways

Genome-wide association studies have identified thousands of common variants associated with an increased risk of neurodegenerative disorders. However, the noncoding localization of these variants has made the assignment of target genes for brain cell types challenging. Genomic approaches that infer chromosomal 3D architecture can link noncoding risk variants and distal gene regulatory elements such as enhancers to gene promoters. By using enhancer-to-promoter interactome maps for human microglia, neurons, and oligodendrocytes, we identified cell-type-specific enrichment of genetic heritability for brain disorders through stratified linkage disequilibrium score regression. Our analysis suggests that genetic heritability for multiple neurodegenerative disorders is enriched at microglial chromatin contact sites, while schizophrenia heritability is predominantly enriched at chromatin contact sites in neurons followed by oligodendrocytes. Through Hi-C coupled multimarker analysis of genomic annotation (H-MAGMA), we identified disease risk genes for Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis and schizophrenia. We found that disease-risk genes were overrepresented in microglia compared to other brain cell types across neurodegenerative conditions and within neurons for schizophrenia. Notably, the microglial risk genes and pathways identified were largely specific to each disease. Our findings reinforce microglia as an important, genetically informed cell type for therapeutic interventions in neurodegenerative conditions and highlight potentially targetable disease-relevant pathways.

Integrated transcriptomic profiling reveals a STING-mediated Type II Interferon signature in SOD1-mutant amyotrophic lateral sclerosis models

Inflammation is a hallmark of amyotrophic lateral sclerosis (ALS), particularly in cases with SOD1 mutations. Using integrative transcriptomics, we analyzed gene expression changes in mouse models throughout progression, human induced-pluripotent stem cells (hiPSCs), and post-mortem spinal cord tissue from ALS patients. We identified a conserved upregulation of interferon (IFN) genes and IFN-stimulating genes (ISGs) in both mouse models and human ALS, with a predominance Type I IFNs (IFN-α/β) in mice and Type II IFNs (IFN-γ) in humans. In mouse models, we observed robust and sustained upregulation of Type I and II ISGs, including ATF3, beginning at disease onset stage and persisting throughout disease progression. Single-cell transcriptomics further pinpointed vascular endothelial cells as a major source of ISGs. Furthermore, we found that the STING-TBK1 axis is essential for the induction of Type II ISGs in ALS, as its deletion impaired their expression. Our study uncovers a conserved ISGs signature across ALS models and patients, highlighting the potential role of innate immune activation in ALS pathogenesis. These findings suggest that ISGs may serve as potential biomarkers and therapeutic targets for ALS.

Using ALS to understand profilin 1's diverse roles in cellular physiology

Profilin is an actin monomer-binding protein whose role in actin polymerization has been studied for nearly 50 years. While its principal biochemical features are now well understood, many questions remain about how profilin controls diverse processes within the cell. Dysregulation of profilin has been implicated in a broad range of human diseases, including neurodegeneration, inflammatory disorders, cardiac disease, and cancer. For example, mutations in the profilin 1 gene (PFN1) can cause amyotrophic lateral sclerosis (ALS), although the precise mechanisms that drive neurodegeneration remain unclear. While initial work suggested proteostasis and actin cytoskeleton defects as the main pathological pathways, multiple novel functions for PFN1 have since been discovered that may also contribute to ALS, including the regulation of nucleocytoplasmic transport, stress granules, mitochondria, and microtubules. Here, we will review these newly discovered roles for PFN1, speculate on their contribution to ALS, and discuss how defects in actin can contribute to these processes. By understanding profilin 1's involvement in ALS pathogenesis, we hope to gain insight into this functionally complex protein with significant influence over cellular physiology.

Micro-Doses of DNP Preserve Motor and Muscle Function with a Period of Functional Recovery in Amyotrophic Lateral Sclerosis Mice

OBJECTIVE

Mitochondrial dysfunction is one of the earliest pathological events observed in amyotrophic lateral sclerosis (ALS). The aim of this study is to evaluate the therapeutic efficacy of 2,4-dinitrophenol (DNP), a mild mitochondrial uncoupler, in an ALS mouse model to provide preclinical proof-of-concept evidence of using DNP as a potential therapeutic drug for ALS.

METHODS

hSOD1G93A mice were treated with 0.5-1.0 mg/kg DNP through daily oral gavage from presymptomatic stage or disease onset until 18 weeks old. Longitudinal behavioral studies were performed weekly or biweekly from 6 to 18 weeks old. In situ muscle contraction measurements in extensor digitorum longus muscles were conducted to evaluate the preservation of contractile force and motor unit numbers in hSOD1G93A mice following DNP treatment. Muscle innervation and inflammatory markers were assessed using immunostaining. Extent of protein oxidation and activation of Akt pathway were also examined.

RESULTS

DNP delayed disease onset; improved motor coordination and muscle performance in vivo; preserved muscle contractile function, neuromuscular junction morphology, and muscle innervation; and reduced inflammation and protein oxidation at 18 weeks old in hSOD1G93A mice. Strikingly, symptomatic hSOD1G93A mice exhibited a period of recovery in running ability at 20 cm/s several weeks after 2,4-dinitrophenol treatment started at disease onset, offering the first observation in disease phenotype reversal using a small molecule.

INTERPRETATION

Our results strongly support that micro-dose DNP may be used as a potential novel treatment for ALS patients, with a possibility for recovery, when used at optimal doses and time of intervention. ANN NEUROL 2025;97:542-557.

Conformational switches in human RNA binding proteins involved in neurodegeneration

Conformational switching in RNA binding proteins (RBPs) is crucial for regulation of RNA processing and transport. Dysregulation or mutations in RBPs and broad RNA processing abnormalities are related to many human diseases including neurodegenerative disorders. Here, we review the role of protein-RNA conformational switches in RBP-RNA complexes. RBP-RNA complexes exhibit wide range of conformational switching depending on the RNA molecule and its ability to induce conformational changes in its partner RBP. We categorize the conformational switches into three groups: rigid body, semi-flexible and full flexible. We also investigate conformational switches in large cellular assemblies including ribosome, spliceosome and RISC complexes. In addition, the role of intrinsic disorder in RBP-RNA conformational switches is discussed. We have also discussed the effect of different disease-causing mutations on conformational switching of proteins associated with neurodegenerative diseases. We believe that this study will enhance our understanding on the role of protein-RNA conformational switches. Furthermore, the availability of a large number of atomic structures of RBP-RNA complexes in near future would facilitate to create a complete repertoire of human RBP-RNA conformational switches.

A Twist in Yeast: New Perspectives for Studying TDP-43 Proteinopathies in S. cerevisiae

TAR DNA-binding protein 43 kDa (TDP-43) proteinopathies are a group of neurodegenerative diseases (NDs) characterized by the abnormal accumulation of the TDP-43 protein in neurons and glial cells. These proteinopathies are associated with several NDs, including amyotrophic lateral sclerosis, frontotemporal lobar degeneration, and some forms of Alzheimer's disease. Yeast models have proven valuable in ND research due to their simplicity, genetic tractability, and the conservation of many cellular processes shared with higher eukaryotes. For several decades, Saccharomyces cerevisiae has been used as a model organism to study the behavior and toxicity of TDP-43, facilitating the identification of genes and pathways that either exacerbate or mitigate its toxic effects. This review will discuss evidence showing that yeast models of TDP-43 exhibit defects in proteostasis, mitochondrial function, autophagy, and RNA metabolism, which are key features of TDP-43-related NDs. Additionally, we will explore how modulating proteins involved in these processes reduce TDP-43 toxicity, aiding in restoring normal TDP-43 function or preventing its pathological aggregation. These findings highlight potential therapeutic targets for the treatment of TDP-43-related diseases.

Mitophagy in Neurodegenerative Diseases: Mechanisms of Action and the Advances of Drug Discovery

Neurodegenerative diseases (NDDs), such as Parkinson's disease (PD) and Alzheimer's disease (AD), are devastating brain diseases and are incurable at the moment. Increasing evidence indicates that NDDs are associated with mitochondrial dysfunction. Mitophagy removes defective or redundant mitochondria to maintain cell homeostasis, whereas deficient mitophagy accelerates the accumulation of damaged mitochondria to mediate the pathologies of NDDs. Therefore, targeting mitophagy has become a valuable therapeutic pathway for the treatment of NDDs. Several mitophagy modulators have been shown to ameliorate neurodegeneration in PD and AD. However, it remains to be further investigated for other NDDs. Here, we describe the mechanism and key signaling pathway of mitophagy and summarize the roles of defective mitophagy on the pathogenesis of NDDs. Further, we underline the development advances of mitophagy modulators for PD and AD therapy, discuss the therapeutic challenges and limitations of the existing modulators, and provide guidelines for mitophagy mechanism exploration and drug design.

Advancements in genetic research and RNA therapy strategies for amyotrophic lateral sclerosis (ALS): current progress and future prospects

This review explores the intricate landscape of neurodegenerative disease research, focusing on Amyotrophic Lateral Sclerosis (ALS) and the intersection of genetics and RNA biology to investigate the causative pathogenetic basis of this fatal disease. ALS is a severe neurodegenerative disease characterized by the progressive loss of motor neurons, leading to muscle weakness and paralysis. Despite significant research advances, the exact cause of ALS remains largely unknown. Thanks to the application of next-generation sequencing (NGS) approaches, it was possible to highlight the fundamental role of rare variants with large effect sizes and involvement of portions of non-coding RNA, providing valuable information on risk prediction, diagnosis, and treatment of age-related diseases, such as ALS. Genetic research has provided valuable insights into the pathophysiology of ALS, leading to the development of targeted therapies such as antisense oligonucleotides (ASOs). Regulatory agencies in several countries are evaluating the commercialization of Qalsody (Tofersen) for SOD1-associated ALS, highlighting the potential of gene-targeted therapies. Furthermore, the emerging significance of microRNAs (miRNAs) and long RNAs are of great interest. MiRNAs have emerged as promising biomarkers for diagnosing ALS and monitoring disease progression. Understanding the role of lncRNAs in the pathogenesis of ALS opens new avenues for therapeutic intervention. However, challenges remain in delivering RNA-based therapeutics to the central nervous system. Advances in genetic screening and personalized medicine hold promise for improving the management of ALS. Ongoing clinical trials use genomic approaches for patient stratification and drug targeting. Further research into the role of non-coding RNAs in the pathogenesis of ALS and their potential as therapeutic targets is crucial to the development of effective treatments for this devastating disease.

Alternative splicing factors and cardiac disease: more than just missplicing?

Alternative splicing (AS) is the process wherein the exons from a single gene are joined in different combinations to produce nonidentical, albeit related, RNA transcripts. This process is important for the development and physiological function of many organs and is particularly important in the heart. Notably, AS has been implicated in cardiac disease and failure, and a growing number of genetic variants in AS factors have been identified in association with cardiac malformation and/or disease. With the field poised to interrogate how these variants affect cardiac development and disease, an understandable point of emphasis will undoubtedly be on downstream target gene missplicing. In this Perspective article, we would like to encourage consideration not only of the potential for novel disease mechanisms, but also for contributions from disruption of the ever-expanding list of nonsplicing functions ascribed to many AS factors. We discuss the emergence of a novel cardiac disease mechanism based on pathogenic RNA granules and speculate on the generality of such a mechanism among localization-disrupting AS factor genetic variants. We also highlight emerging nonsplicing functions attributed to several AS factors with cardiac disease-associated genetic variants in the hopes of pointing to avenues for exploration of mechanisms that may contribute to disease alongside target gene missplicing.

Muscle Matters: Transforming Amyotrophic Lateral Sclerosis Diagnostics with Next-Gen Biosensors and Smart Detection

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that primarily targets the motor system, causing patients' speech and swallowing ability to rapidly deteriorate. Although ALS is usually classified into familial and sporadic forms, diagnosing it can be extremely difficult due to the absence of definitive biomarkers, often resulting in delays in diagnosis. Current diagnostic practices rely heavily on clinical assessments that indicate damage to both upper motor neurons (UMNs) and lower motor neurons (LMNs). This includes comprehensive physical examinations, electromyography (EMG) to assess neuromuscular function, and the exclusion of other similar conditions such as cervical spondylotic myelopathy, multifocal motor neuropathy, and Kennedy's disease through appropriate diagnostic procedures. The urgent need for specific biomarkers is critical for timely diagnosis and therapeutic advancements in ALS management. While many recent developments in research have not yet translated into direct patient benefits, the recognition of ALS as a complex disease is beginning to influence clinical practice significantly. Optimal management strategies emphasize on symptom control and improving the quality of life for patients within a holistic healthcare framework. This review provides a comprehensive overview of ALS, delving into its pathophysiology, clinical symptoms, and the latest advancements in detection methods that utilize traditional approaches, innovative biosensors, and smart diagnostic technologies. It discusses various treatment options available for ALS while exploring future developments that may enhance patient screening and improve clinical outcomes. By integrating assessments into the underlying mechanisms of the disease with cutting-edge diagnostic approaches, this review aims to contribute meaningfully to ongoing efforts to optimize ALS management and therapeutic strategies, ultimately improving patient care and outcomes.

How is the Amyloid Fold Built? Polymorphism and the Microscopic Mechanisms of Fibril Assembly

For a given protein sequence, many, up to sometimes hundreds of different amyloid fibril folds, can be formed in vitro. Yet, fibrils extracted from, or found in, human tissue, usually at the end of a long disease process, are often structurally homogeneous. Through monitoring of amyloid assembly reactions in vitro, the scientific community has gained a detailed understanding of the kinetic mechanisms of fibril assembly and the rates at which the different processes involved occur. However, how this kinetic information relates to the structural changes as a protein transforms from its initial, native structure to the canonical cross-β structure of amyloid remain obscure. While cryoEM has yielded a plethora of high-resolution information that portray a vast variety of fibril structures, there remains little knowledge of how and why each particular structure resulted. Recent work has demonstrated that fibril structures can change over an assembly time course, despite the different fibril types having similar thermodynamic stability. This points to kinetic control of the fibrils formed, with structures that initiate or elongate faster becoming the dominant products of assembly. Annotating kinetic assembly mechanisms alongside structural analysis of the fibrils formed is required to truly understand the molecular mechanisms of amyloid formation. However, this is a complicated task. In this review, we discuss how embracing this challenge could open new frontiers in amyloid research and new opportunities for therapy.

Amyotrophic lateral sclerosis caused by FUS mutations: advances with broad implications

Autosomal dominant mutations in the gene encoding the DNA and RNA binding protein FUS are a cause of amyotrophic lateral sclerosis (ALS), and about 0·3-0·9% of patients with ALS are FUS mutation carriers. FUS-mutation-associated ALS (FUS-ALS) is characterised by early onset and rapid progression, compared with other forms of ALS. However, different pathogenic mutations in FUS can result in markedly different age at symptom onset and rate of disease progression. Most FUS mutations disrupt its nuclear localisation, leading to its cytoplasmic accumulation in the CNS. FUS also forms inclusions in around 5% of patients with the related neurodegenerative condition frontotemporal dementia. However, there are key differences between the two diseases at the genetic and neuropathological level, which suggest distinct pathogenic processes. Experimental models have uncovered potential pathogenic mechanisms in FUS-ALS and informed therapeutic strategies that are currently in development, including the silencing of FUS expression using an intrathecally administered antisense oligonucleotide.

A special focus on polyadenylation and alternative polyadenylation in neurodegenerative diseases: A systematic review

Neurodegenerative diseases (NDDs) are one of the prevailing conditions characterized by progressive neuronal loss. Polyadenylation (PA) and alternative polyadenylation (APA) are the two main post-transcriptional events that regulate neuronal gene expression and protein production. This systematic review analyzed the available literature on the role of PA and APA in NDDs, with an emphasis on their contributions to disease development. A comprehensive literature search was performed using the PubMed, Scopus, Cochrane, Google Scholar, Embase, Web of Science, and ProQuest databases. The search strategy was developed based on the framework introduced by Arksey and O'Malley and supplemented by the inclusion and exclusion criteria. The study selection was performed by two independent reviewers. Extraction and data organization were performed in accordance with the predefined variables. Subsequently, quantitative and qualitative analyses were performed. Forty-seven studies were included, related to a variety of NDDs, namely Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Disease induction was performed using different models, including human tissues, animal models, and cultured cells. Most investigations were related to PA, although some were related to APA or both. Amyloid precursor protein (APP), Tau, SNCA, and STMN2 were the major genes identified; most of the altered PA patterns were related to mRNA stability and translation efficiency. This review particularly underscores the key roles of PA and APA in the pathogenesis of NDDs through their mechanisms that contribute to gene expression dysregulation, protein aggregation, and neuronal dysfunction. Insights into these mechanisms may lead to new therapeutic strategies focused on the modulation of PA and APA activities. Further research is required to investigate the translational potential of targeting these pathways for NDD treatment.

RNA dysregulation in neurodegenerative diseases

Dysregulation of RNA processing has in recent years emerged as a significant contributor to neurodegeneration. The diverse mechanisms and molecular functions underlying RNA processing underscore the essential role of RNA regulation in maintaining neuronal health and function. RNA molecules are bound by RNA-binding proteins (RBPs), and interactions between RNAs and RBPs are commonly affected in neurodegeneration. In this review, we highlight recent progress in understanding dysregulated RNA-processing pathways and the causes of RBP dysfunction across various neurodegenerative diseases. We discuss both established and emerging mechanisms of RNA-mediated neuropathogenesis in this rapidly evolving field. Furthermore, we explore the development of potential RNA-targeting therapeutic approaches for the treatment of neurodegenerative diseases.

Ubiquitin-Proteasome-Mediated Protein Degradation and Disorders of the Central Nervous System

Ubiquitin-proteasome-mediated proteolysis post-translationally regulates the amounts of many proteins that are critical for the normal physiology of the central nervous system. Research carried out over the last several years has revealed a role for components of the ubiquitin-proteasome pathway (UPP) in many neurodegenerative diseases such as Parkinson's disease and Huntington's disease. Studies have also shown a role for the UPP in mental disorders such as schizophrenia and autism. Even though dysregulation of protein degradation by the UPP is a contributory factor to the pathology underlying many nervous system disorders, the association between the components of the UPP and these diseases is far from simple. In this review, we discuss the connections between the UPP and some of the major mental disorders and neurodegenerative diseases.

Application of antisense oligonucleotide drugs in amyotrophic lateral sclerosis and Huntington's disease

Amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD) are diverse in clinical presentation and are caused by complex and multiple factors, including genetic mutations and environmental factors. Numerous therapeutic approaches have been developed based on the genetic causes and potential mechanisms of ALS and HD. Currently, available treatments for various neurodegenerative diseases can alleviate symptoms but do not provide a definitive cure. Gene therapy, which aims to modify or express specific proteins for neuroprotection or correction, is considered a powerful tool in managing neurodegenerative conditions. To date, antisense oligonucleotide (ASO) drugs targeting the pathological genes associated with ALS and HD have shown promising results in numerous animal studies and several clinical trials. This review provides a comprehensive overview of the development, mechanisms of action, limitations, and clinical applications of ASO drugs in neurodegenerative diseases, with a specific focus on ALS and HD therapeutic strategies.

Ataxin-2 polyglutamine expansions aberrantly sequester TDP-43 ribonucleoprotein condensates disrupting mRNA transport and local translation in neurons

Altered RNA metabolism and misregulation of transactive response DNA-binding protein of 43 kDa (TDP-43), an essential RNA-binding protein (RBP), define amyotrophic lateral sclerosis (ALS). Intermediate-length polyglutamine (polyQ) expansions of Ataxin-2, a like-Sm (LSm) RBP, are associated with increased risk for ALS, but the underlying biological mechanisms remain unknown. Here, we studied the spatiotemporal dynamics and mRNA regulatory functions of TDP-43 and Ataxin-2 ribonucleoprotein (RNP) condensates in rodent (rat) primary cortical neurons and mouse motor neuron axons in vivo. We report that Ataxin-2 polyQ expansions aberrantly sequester TDP-43 within RNP condensates and disrupt both its motility along the axon and liquid-like properties. We provide evidence that Ataxin-2 governs motility and translation of neuronal RNP condensates and that Ataxin-2 polyQ expansions fundamentally perturb spatial localization of mRNA and suppress local translation. Overall, our results support a model in which Ataxin-2 polyQ expansions disrupt stability, localization, and/or translation of critical axonal and cytoskeletal mRNAs, particularly important for motor neuron integrity.

Swift induction of human spinal lower motor neurons and robust ALS cell screening via single-cell imaging

This study introduces a novel method for rapidly and efficiently inducing human spinal lower motor neurons (LMNs) from induced pluripotent stem cells (iPSCs) to eventually elucidate the pathomechanisms of amyotrophic lateral sclerosis (ALS) and facilitate drug screening. Previous methods were limited by low induction efficiency, poor LMN purity, or labor-intensive induction and evaluation processes. Our protocol overcomes these challenges, achieving around 80% induction efficiency within just two weeks by combining a small molecule-based approach with transcription factor transduction. Moreover, to exclude non-LMN cells from the analysis, we utilized time-lapse microscopy and machine learning to analyze the morphology and viability of iPSC-derived LMNs on a single-cell basis, establishing an effective pathophysiological evaluation system. This rapid, efficient, and streamlined protocol, along with our single-cell-based evaluation method, enables large-scale analysis and drug screening using iPSC-derived motor neurons.

The Current Potential Pathogenesis of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease mainly characterized by the accumulation of ubiquitinated proteins in the affected motor neurons. At present, the accurate pathogenesis of ALS remains unclear and there are still no effective treatment measures for ALS. The potential pathogenesis of ALS mainly includes the misfolding of some pathogenic proteins, the genetic variation, mitochondrial dysfunction, autophagy disorders, neuroinflammation, the misregulation of RNA, the altered axonal transport, and gut microbial dysbiosis. Exploring the pathogenesis of ALS is a critical step in searching for the effective therapeutic approaches. The current studies suggested that the genetic variation, gut microbial dysbiosis, the activation of glial cells, and the transportation disorder of extracellular vesicles may play some important roles in the pathogenesis of ALS. This review conducts a systematic review of these current potential promising topics closely related to the pathogenesis of ALS; it aims to provide some new evidences and clues for searching the novel treatment measures of ALS.

Artificial Intelligence-Assisted Comparative Analysis of the Overlapping Molecular Pathophysiology of Alzheimer's Disease, Amyotrophic Lateral Sclerosis, and Frontotemporal Dementia

The overlapping molecular pathophysiology of Alzheimer's Disease (AD), Amyotrophic Lateral Sclerosis (ALS), and Frontotemporal Dementia (FTD) was analyzed using relationships from a knowledge graph of 33+ million biomedical journal articles. The unsupervised learning rank aggregation algorithm from SemNet 2.0 compared the most important amino acid, peptide, and protein (AAPP) nodes connected to AD, ALS, or FTD. FTD shared 99.9% of its nodes with ALS and AD; AD shared 64.2% of its nodes with FTD and ALS; and ALS shared 68.3% of its nodes with AD and FTD. The results were validated and mapped to functional biological processes using supervised human supervision and an external large language model. The overall percentages of mapped intersecting biological processes were as follows: inflammation and immune response, 19%; synapse and neurotransmission, 19%; cell cycle, 15%; protein aggregation, 12%; membrane regulation, 11%; stress response and regulation, 9%; and gene regulation, 4%. Once normalized for node count, biological mappings for cell cycle regulation and stress response were more prominent in the intersection of AD and FTD. Protein aggregation, gene regulation, and energetics were more prominent in the intersection of ALS and FTD. Synapse and neurotransmission, membrane regulation, and inflammation and immune response were greater at the intersection of AD and ALS. Given the extensive molecular pathophysiology overlap, small differences in regulation, genetic, or environmental factors likely shape the underlying expressed disease phenotype. The results help prioritize testable hypotheses for future clinical or experimental research.

Amino acids modulate liquid-liquid phase separation in vitro and in vivo by regulating protein-protein interactions

Liquid-liquid phase separation (LLPS) is an intracellular process widely used by cells for many key biological functions. It occurs in complex and crowded environments, where amino acids (AAs) are vital components. We have found that AAs render the net interaction between proteins more repulsive. Here, we find that some AAs efficiently suppress LLPS in test tubes (in vitro). We then screen all the proteinogenic AAs and find that three specific AAs, including proline, glutamine, and glycine, significantly suppressed the formation of stress granules (SGs) in U2OS and HeLa cell lines (in vivo) irrespective of stress types. We also observe the effect in primary fibroblast cells, a viable cell model for neurodegenerative disorders. Kinetic studies by live-cell microscopy show that the presence of AAs not only slows down the formation but also decreases the saturating number and prevents the coalescence of SGs. We finally use sedimentation-diffusion equilibrium analytical ultracentrifuge (SE-AUC) to demonstrate that the suppression effects of AAs on LLPS may be due to their modulation in protein-protein and RNA-RNA interactions. Overall, this study reveals an underappreciated role of cellular AAs, which may find biomedical applications, especially in treating SG-associated diseases.

Molecular mechanisms of neurofilament alterations and its application in assessing neurodegenerative disorders

Neurofilaments are intermediate filaments present in neurons. These provide structural support and maintain the size and shape of the neurons. Dysregulation, mutation, and aggregation of neurofilaments raise the levels of these proteins in the blood and cerebrospinal fluid (CSF), which are characteristic features of axonal damage and certain rare neurological diseases, such as Giant Axonal Neuropathy and Charcot-Mare-Tooth disease. Understanding the structure, dynamics, and function of neurofilaments has been greatly enhanced by a diverse range of biochemical and preclinical investigations conducted over more than four decades. Recently, there has been a resurgence of interest in post-translational modifications of neurofilaments, such as phosphorylation, aggregation, mutation, oxidation, etc. Over the past twenty years, several rare disorders have been studied from structural alterations of neurofilaments. These disorders are monitored by fluid biomarkers such as neurofilament light chains. Currently, there are many tools, such as Enzyme-Linked Immunosorbent Assay, Electrochemiluminescence Assay, Single-Molecule Array, Western/immunoblotting, etc., in use to assess the neurofilament proteins in Blood and CSF. However, all these techniques utilize expensive, non-specific, or antibody-based methods, which make them unsuitable for routine screening of neurodegenerative disorders. This provides room to search for newer sensitive, cost-effective, point-of-care tools for rapid screening of the disease. For a long time, the molecular mechanisms of neurofilaments have been poorly understood due to insufficient research attempts, and a deeper understanding of them remains elusive. Therefore, this review aims to highlight the available literature on molecular mechanisms of neurofilaments and the function of neurofilaments in axonal transport, axonal conduction, axonal growth, and neurofilament aggregation, respectively. Further, this review discusses the role of neurofilaments as potential biomarkers for the identification of several neurodegenerative diseases in clinical laboratory practice.

Selective Inhibition of Cytosolic PARylation via PARG99: A Targeted Approach for Mitigating FUS-associated Neurodegeneration

Neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) are characterized by complex etiologies, often involving disruptions in functions of RNA/DNA binding proteins (RDBPs) such as FUS and TDP-43. The cytosolic mislocalization and aggregation of these proteins are linked to accumulation of unresolved stress granules (SGs), which exacerbate the disease progression. Poly-ADP-ribose polymerase (PARP)-mediated PARylation plays a critical role in this pathological cascade, making it a potential target for intervention. However, conventional PARP inhibitors are limited by their detrimental effects on DNA repair pathways, which are already compromised in ALS. To address this limitation, we investigated a strategy focused on targeting the cytosolic compartment by expressing the cytosol-specific, natural PAR- glycohydrolase (PARG) isoform, PARG99. Using ALS patient derived FUS mutant induced pluripotent cells (iPSCs) and differentiated neurons, we observed elevated levels of FUS in insoluble fractions in mutant cells compared to mutation-corrected isogenic lines. The insoluble FUS as well as TDP-43 levels increased further in sodium arsenite-treated or oxidatively stressed cells, correlating with accumulation of unresolved SGs. Notably, both PARG99 and PARP inhibitors reduced SG formation and insoluble FUS levels, however, PARG99 treated cells exhibited significantly lower DNA damage markers and improved viability under oxidative and arsenite stress. This study highlights the potential of PARG99 as a cytosol-specific intervention to mitigate FUS-associated toxicity while preserving critical nuclear DNA repair mechanisms, offering a promising strategy for addressing the underlying pathology of ALS and potentially other SG-associated neurodegenerative diseases.

Axonal transcriptome reveals upregulation of PLK1 as a protective mechanism in response to increased DNA damage in FUS P525L spinal motor neurons

Mutations in the gene FUSED IN SARCOMA ( FUS ) are among the most frequently occurring genetic forms of amyotrophic lateral sclerosis (ALS). Early pathogenesis of FUS -ALS involves impaired DNA damage response and axonal degeneration. However, it is still poorly understood how these gene mutations lead to selective spinal motor neuron (MN) degeneration and how nuclear and axonal phenotypes are linked. To specifically address this, we applied a compartment specific RNA-sequencing approach using microfluidic chambers to generate axonal as well as somatodendritic compartment-specific profiles from isogenic induced pluripotent stem cells (iPSCs)-derived MNs. We demonstrate high purity of axonal and soma fractions and show that the axonal transcriptome is unique and distinct from that of somas including significantly fewer number of transcripts. Functional enrichment analysis revealed that differentially expressed genes (DEGs) in axons were mainly enriched in key pathways like RNA metabolism and DNA damage, complementing our knowledge of early phenotypes in ALS pathogenesis and known functions of FUS. In addition, we demonstrate a strong enrichment for cell cycle associated genes including significant upregulation of polo-like kinase 1 (PLK1) in FUS P525L mutant MNs. PLK1 was increased upon DNA damage induction and PLK1 inhibition further increased the number of DNA damage foci in etoposide-treated cells, an effect that was diminished in case of FUS mutant MNs. In contrast, inhibition of PLK1 increased late apoptotic or necrosis-induced neuronal cell death in mutant neurons. Taken together, our findings provide insights into compartment-specific transcriptomics in human FUS -ALS MNs and we propose that specific upregulation of PLK1 might represent an early event in the pathogenesis of ALS, possibly modulating DNA damage response and other associated pathways.

Axonopathy Underlying Amyotrophic Lateral Sclerosis: Unraveling Complex Pathways and Therapeutic Insights

Amyotrophic Lateral Sclerosis (ALS) is a complex neurodegenerative disorder characterized by progressive axonopathy, jointly leading to the dying back of the motor neuron, disrupting both nerve signaling and motor control. In this review, we highlight the roles of axonopathy in ALS progression, driven by the interplay of multiple factors including defective trafficking machinery, protein aggregation, and mitochondrial dysfunction. Dysfunctional intracellular transport, caused by disruptions in microtubules, molecular motors, and adaptors, has been identified as a key contributor to disease progression. Aberrant protein aggregation involving TDP-43, FUS, SOD1, and dipeptide repeat proteins further amplifies neuronal toxicity. Mitochondrial defects lead to ATP depletion, oxidative stress, and Ca2+ imbalance, which are regarded as key factors underlying the loss of neuromuscular junctions and axonopathy. Mitigating these defects through interventions including neurotrophic treatments offers therapeutic potential. Collaborative research efforts aim to unravel ALS complexities, opening avenues for holistic interventions that target diverse pathological mechanisms.

Inhibition of glycolytic reprogramming suppresses innate immune-mediated inflammation in experimental amyotrophic lateral sclerosis

BACKGROUND

Innate immune activation has been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). However, metabolic pathways that govern this bioenergetically demanding process in ALS remains elusive. Here we investigated whether and how immunometabolic transformation of innate immune cells contributes to disease progression in an experimental model of this neurodegenerative disease.

METHODS

We utilized multidimensional flow cytometry and integrative metabolomics to characterize the immunometabolic phenotype of circulating and spinal cord innate immune cells in the B6SJL-Tg(SOD1*G93A)1Gur/J model of ALS (SOD1-G93A) at various disease stages (before vs. after the onset of motor dysfunction). Behavioral and survival analyses were also conducted to determine the impact of an energy-regulating compound on innate immune cell metabolism, inflammation, and disease development.

RESULTS

Temporally coordinated accumulation of circulating inflammatory Ly6C + monocytes and spinal cord F4/80 + CD45hi infiltrates precedes the onset of motor dysfunction in SOD1-G93A mice. Subsequent metabolomic analysis reveals that this phenomenon is accompanied by glycolytic reprogramming of spinal cord inflammatory CD11b + cells, comprising both resident F4/80 + CD45low microglia and F4/80 + CD45hi infiltrates. Furthermore, pharmacologic inhibition of glycolysis by ZLN005, a small molecule activator of Ppargc1a, restrains inflammatory glycolytic activation of spinal cord CD11b + cells, enhances motor function, and prolongs survival in SOD1-G93A mice.

CONCLUSIONS

These observations suggest that modulation of inflammatory glycolytic reprogramming of innate immune cells may represent a promising therapeutic approach in ALS.

Challenges in Therapeutically Targeting the RNA-Recognition Motif

The RNA recognition motif (RRM) is the most common RNA binding domain found in the human proteome. RRM domains provide RNA-binding proteins with sequence specific RNA recognition allowing them to participate in RNA-centric processes such as mRNA maturation, translation initiation, splicing, and RNA degradation. They are drivers of various diseases through overexpression or mutation, making them attractive therapeutic targets and addressing these proteins through their RRM domains with chemical compounds is gaining ever more attention. However, it is still very challenging to find selective and potent RNA-competitors due to the small size of the domain and high structural conservation of its RNA binding interface. Despite these challenges, a selection of compounds has been reported for several RRM containing proteins, but often with limited biophysical evidence and low selectivity. A solution to selectively targeting RRM domains might be through avoiding the RNA-binding surface altogether, but rather look for composite pockets formed with other proteins or for protein-protein interaction sites that regulate the target's activity but are less conserved. Alternative modalities, such as oligonucleotides, peptides, and molecular glues, are exciting new approaches to address these challenging targets and achieve the goal of therapeutic intervention at the RNA regulatory level.

Dynamic Expression of Genes Encoding Ubiquitin Conjugating Enzymes (E2s) During Neuronal Differentiation and Maturation: Implications for Neurodevelopmental Disorders and Neurodegenerative Diseases

Background: The ubiquitination process plays a crucial role in neuronal differentiation and function. Numerous studies have focused on the expression and functions of E3 ligases during these different stages, far fewer on E2 conjugating enzymes. In mice, as in humans, these E2s belong to 17 conjugating enzyme families. Objectives: We analyzed by real-time PCR the expression dynamics of all known E2 genes during an in vitro differentiation of mouse hippocampal neuronal cultures, and after, we analyzed their stimulation with N-methyl-D-aspartate (NMDA). Results: We found that 36 of the 38 E2 genes were expressed in hippocampal neurons. Many were up-regulated during neuritogenesis and/or synaptogenesis stages, such as Ube2h, Ube2b, and Aktip. Rapid and delayed responses to NMDA stimulation were associated with the increased expression of several E2 genes, such as Ube2i, the SUMO-conjugating E2 enzyme. We also observed similar expression profiles within the same E2 gene family, consistent with the presence of similar transcription factor binding sites in their respective promoter sequences. Conclusions: Our study indicates that specific expression profiles of E2 genes are correlated with changes in neuronal differentiation and activity. A better understanding of the regulation and function of E2s is needed to better understand the role played by the ubiquitination process in physiological mechanisms and pathophysiological alterations involved in neurodevelopmental or neurodegenerative diseases.

TNFα prevents FGF4-mediated rescue of astrocyte dysfunction and reactivity in human ALS models

Astrocytes play a crucial role in the onset and progression of amyotrophic lateral sclerosis (ALS), a fatal disorder marked by the degeneration of motor neurons (MNs) in the central nervous system. Although astrocytes in ALS are known to be toxic to MNs, the pathological changes leading to their neurotoxic phenotype remain poorly understood. In this study, we generated human astrocytes from induced pluripotent stem cells (iPSCs) carrying the ALS-associated A4V mutation in superoxide dismutase 1 (SOD1) to examine early cellular pathways and network changes. Proteomic analysis revealed that ALS astrocytes are both dysfunctional and reactive compared to control astrocytes. We identified significant alterations in the levels of proteins linked to ALS pathology and the innate immune cGAS-STING pathway. Furthermore, we found that ALS astrocyte reactivity differs from that of control astrocytes treated with tumor necrosis factor alpha (TNFα), a key cytokine in inflammatory reactions. We then evaluated the potential of fibroblast growth factor (FGF) 2, 4, 16, and 18 to reverse ALS astrocyte phenotype. Among these, FGF4 successfully reversed ALS astrocyte dysfunction and reactivity in vitro. When delivered to the spinal cord of the SOD1G93A mouse model of ALS, FGF4 lowered astrocyte reactivity. However, this was not sufficient to protect MNs from cell death. Further analysis indicated that TNFα abrogated the reactivity reduction achieved by FGF4, suggesting that complete rescue of the ALS phenotype by FGF4 is hindered by ongoing complex neuroinflammatory processes in vivo. In summary, our data demonstrate that astrocytes generated from ALS iPSCs are inherently dysfunctional and exhibit an immune reactive phenotype. Effectively targeting astrocyte dysfunction and reactivity in vivo may help mitigate ALS and prevent MN death.

Exercise, disease state and sex influence the beneficial effects of Fn14-depletion on survival and muscle pathology in the SOD1G93A amyotrophic lateral sclerosis (ALS) mouse model

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a devastating and incurable neurodegenerative disease. Accumulating evidence strongly suggests that intrinsic muscle defects exist and contribute to disease progression, including imbalances in whole-body metabolic homeostasis. We have previously reported that tumour necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and fibroblast growth factor inducible 14 (Fn14) are significantly upregulated in skeletal muscle of the SOD1G93A ALS mouse model. While antagonising TWEAK did not impact survival, we did observe positive effects in skeletal muscle. Given that Fn14 has been proposed as the main effector of the TWEAK/Fn14 activity and that Fn14 can act independently from TWEAK in muscle, we suggest that manipulating Fn14 instead of TWEAK in the SOD1G93A ALS mice could lead to differential and potentially improved benefits.

METHODS

We thus investigated the contribution of Fn14 to disease phenotypes in the SOD1G93A ALS mice. To do so, Fn14 knockout mice (Fn14-/-) were crossed onto the SOD1G93A background to generate SOD1G93A;Fn14-/- mice. Investigations were performed on both unexercised and exercised (rotarod and/or grid test) animals (wild type (WT), Fn14-/-, SOD1G93A and SOD1G93A;Fn14-/-).

RESULTS

Here, we firstly confirm that the TWEAK/Fn14 pathway is dysregulated in skeletal muscle of SOD1G93A mice. We then show that Fn14-depleted SOD1G93A mice display increased lifespan, myofiber size, neuromuscular junction endplate area as well as altered expression of known molecular effectors of the TWEAK/Fn14 pathway, without an impact on motor function. Importantly, we also observe a complex interaction between exercise (rotarod and grid test), genotype, disease state and sex that influences the overall effects of Fn14 deletion on survival, expression of known molecular effectors of the TWEAK/Fn14 pathway, expression of myosin heavy chain isoforms and myofiber size.

CONCLUSIONS

Our study provides further insights on the different roles of the TWEAK/Fn14 pathway in pathological skeletal muscle and how they can be influenced by age, disease, sex and exercise. This is particularly relevant in the ALS field, where combinatorial therapies that include exercise regimens are currently being explored. As such, a better understanding and consideration of the interactions between treatments, muscle metabolism, sex and exercise will be of importance in future studies.

Transcript errors generate amyloid-like proteins in huwman cells

Aging is characterized by the accumulation of proteins that display amyloid-like behavior. However, the molecular mechanisms by which these proteins arise remain unclear. Here, we demonstrate that amyloid-like proteins are produced in a variety of human cell types, including stem cells, brain organoids and fully differentiated neurons by mistakes that occur in messenger RNA molecules. Some of these mistakes generate mutant proteins already known to cause disease, while others generate proteins that have not been observed before. Moreover, we show that these mistakes increase when cells are exposed to DNA damage, a major hallmark of human aging. When taken together, these experiments suggest a mechanistic link between the normal aging process and age-related diseases.

Hippocampal aggregation signatures of pathogenic UBQLN2 in amyotrophic lateral sclerosis and frontotemporal dementia

Pathogenic variants in the UBQLN2 gene cause X-linked dominant amyotrophic lateral sclerosis and/or frontotemporal dementia characterized by ubiquilin 2 aggregates in neurons of the motor cortex, hippocampus and spinal cord. However, ubiquilin 2 neuropathology is also seen in sporadic and familial amyotrophic lateral sclerosis and/or frontotemporal dementia cases not caused by UBQLN2 pathogenic variants, particularly C9orf72-linked cases. This makes the mechanistic role of mutant ubiquilin 2 protein and the value of ubiquilin 2 pathology for predicting genotype unclear. Here we examine a cohort of 44 genotypically diverse amyotrophic lateral sclerosis cases with or without frontotemporal dementia, including eight cases with UBQLN2 variants [resulting in p.S222G, p.P497H, p.P506S, p.T487I (two cases) and p.P497L (three cases)]. Using multiplexed (five-label) fluorescent immunohistochemistry, we mapped the co-localization of ubiquilin 2 with phosphorylated TDP-43, dipeptide repeat aggregates and p62 in the hippocampus of controls (n = 6), or amyotrophic lateral sclerosis with or without frontotemporal dementia in sporadic (n = 20), unknown familial (n = 3), SOD1-linked (n = 1), FUS-linked (n = 1), C9orf72-linked (n = 5) and UBQLN2-linked (n = 8) cases. We differentiate between (i) ubiquilin 2 aggregation together with phosphorylated TDP-43 or dipeptide repeat proteins; and (ii) ubiquilin 2 self-aggregation promoted by UBQLN2 pathogenic variants that cause amyotrophic lateral sclerosis and/or frontotemporal dementia. Overall, we describe a hippocampal protein aggregation signature that fully distinguishes mutant from wild-type ubiquilin 2 in amyotrophic lateral sclerosis with or without frontotemporal dementia, whereby mutant ubiquilin 2 is more prone than wild-type to aggregate independently of driving factors. This neuropathological signature can be used to assess the pathogenicity of UBQLN2 gene variants and to understand the mechanisms of UBQLN2-linked disease.

The genetics of amyotrophic lateral sclerosis

PURPOSE OF REVIEW

Amyotrophic lateral sclerosis (ALS) has a strong genetic basis, but the genetic landscape of ALS appears to be complex. The purpose of this article is to review recent developments in the genetics of ALS.

RECENT FINDINGS

Large-scale genetic studies have uncovered more than 40 genes contributing to ALS susceptibility. Both rare variants with variable effect size and more common variants with small effect size have been identified. The most common ALS genes are C9orf72 , SOD1 , TARDBP and FUS . Some of the causative genes of ALS are shared with frontotemporal dementia, confirming the molecular link between both diseases. Access to diagnostic gene testing for ALS has to improve, as effective gene silencing therapies for some genetic subtypes of ALS are emerging, but there is no consensus about which genes to test for.

SUMMARY

Our knowledge about the genetic basis of ALS has improved and the first effective gene silencing therapies for specific genetic subtypes of ALS are underway. These therapeutic advances underline the need for better access to gene testing for people with ALS. Further research is needed to further map the genetic heterogeneity of ALS and to establish the best strategy for gene testing in a clinical setting.

Promising animal models for amyotrophic lateral sclerosis drug discovery: a comprehensive update

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neurons. Several animal models have been generated to understand ALS pathogenesis. They have provided valuable insight into disease mechanisms and the development of therapeutic strategies.

AREAS COVERED

In this review, the authors provide a concise overview of simple genetic model organisms, including C. elegans, Drosophila, zebrafish, and mouse genetic models that have been generated to study ALS. They emphasize the benefits of each model and their application in translational research for discovering new chemicals, gene therapy approaches, and antibody-based strategies for treating ALS.

EXPERT OPINION

Significant progress is being made in identifying new therapeutic targets for ALS. This progress is being enabled by promising animal models of the disease using increasingly effective genetic and pharmacological strategies. There are still challenges to be overcome in order to achieve improved success rates for translating drugs from animal models to clinics for treating ALS. Several promising future directions include the establishment of novel preclinical protocol standards, as well as the combination of animal models with human induced pluripotent stem cells (iPSCs).

Gut microbiota immune cross-talk in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by the loss of motor neurons. While there has been significant progress in defining the genetic contributions to ALS, greater than 90 ​% of cases are sporadic, which suggests an environmental component. The gut microbiota is altered in ALS and is an ecological factor that contributes to disease by modulating immunologic, metabolic, and neuronal signaling. Depleting the microbiome worsens disease in the SOD1 ALS animal model, while it ameliorates disease in the C9orf72 model of ALS, indicating critical subtype-specific interactions. Furthermore, administering beneficial microbiota or microbial metabolites can slow disease progression in animal models. This review discusses the current state of microbiome research in ALS, including interactions with different ALS subtypes, evidence in animal models and human studies, key immunologic and metabolomic mediators, and a path toward microbiome-based therapies for ALS.