The Overlapping Genetics of Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

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.

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.

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.

The genetics of neurodegenerative diseases is the genetics of age-related damage clearance failure

In this perspective we draw together the data from the genome wide association studies for Alzheimer's disease, Parkinson's disease and the tauopathies and reach the conclusion that in each case, most of the risk loci are involved in the clearance of the deposited proteins: in Alzheimer's disease, the microglial removal of Aβ, in the synucleinopathies, the lysosomal clearance of synuclein and in the tauopathies, the removal of tau protein by the ubiquitin proteasome. We make the point that most loci identified through genome wide association studies are not strictly pathogenic but rather relate to failures to remove age related damage. We discuss these issues in the context of copathologies in elderly individuals and the prediction of disease through polygenic risk score analysis at different ages. Finally, we discuss what analytic approaches are needed now that we have adequately sized case control analyses in white populations.

Identification of a pathogenic mutation in ARPP21 in patients with amyotrophic lateral sclerosis

BACKGROUND AND OBJECTIVE

Between 5% and 10% of amyotrophic lateral sclerosis (ALS) cases have a family history of the disease, 30% of which do not have an identifiable underlying genetic cause after a comprehensive study of the known ALS-related genes. Based on a significantly increased incidence of ALS in a small geographical region from Spain, the aim of this work was to identify novel ALS-related genes in ALS cases with negative genetic testing.

METHODS

We detected an increased incidence of both sporadic and, especially, familial ALS cases in a small region from Spain compared with available demographic and epidemiological data. We performed whole genome sequencing in a group of 12 patients with ALS (5 of them familial) from this unique area. We expanded the study to include affected family members and additional cases from a wider surrounding region.

RESULTS

We identified a shared missense mutation (c.1586C>T; p.Pro529Leu) in the cyclic AMP regulated phosphoprotein 21 (ARPP21) gene that encodes an RNA-binding protein, in a total of 10 patients with ALS from 7 unrelated families. No mutations were found in other ALS-causing genes.

CONCLUSIONS

While previous studies have dismissed a causal role of ARPP21 in ALS, our results strongly support ARPP21 as a novel ALS-causing gene.

Epigenetics in Neurodegenerative Diseases

Healthy brain functioning requires a continuous fine-tuning of gene expression, involving changes in the epigenetic landscape and 3D chromatin organization. Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD) are three multifactorial neurodegenerative diseases (NDDs) that are partially explained by genetics (gene mutations and genetic risk factors) and influenced by non-genetic factors (i.e., aging, lifestyle, and environmental conditions). Examining comprehensive studies of global and locus-specific (epi)genomic and transcriptomic alterations in human and mouse brain samples at the cell-type resolution has uncovered important phenomena associated with AD. First, DNA methylation and histone marks at promoters contribute to transcriptional dysregulation of genes that are directly implicated in AD pathogenesis (i.e., APP), neuroplasticity and cognition (i.e., PSD95), and microglial activation (i.e., TREM2). Second, the presence of AD genetic risk variants in cell-type-specific distal enhancers (i.e., BIN1 in microglia) alters transcription, presumably by disrupting associated enhancer-promoter interactions and chromatin looping. Third, epigenomic erosion is associated with widespread transcriptional disruption and cell identity loss. And fourth, aging, high cholesterol, air pollution, and pesticides have emerged as potential drivers of AD by inducing locus-specific and global epigenetic modifications that impact key AD-related pathways. Epigenetic studies in ALS/FTD also provide evidence that genetic and non-genetic factors alter gene expression profiles in neurons and astrocytes through aberrant epigenetic mechanisms. We additionally overview the recent development of potential new therapeutic strategies involving (epi)genetic editing and the use of small chromatin-modifying molecules (epidrugs).

Clinicopathological analysis of NEK1 variants in amyotrophic lateral sclerosis

Many genes have been linked to amyotrophic lateral sclerosis (ALS), including never in mitosis A (NIMA)-related kinase 1 (NEK1), a serine/threonine kinase that plays a key role in several cellular functions, such as DNA damage response and cell cycle regulation. Whole-exome sequencing studies have shown that NEK1 mutations are associated with an increased risk for ALS, where a significant enrichment of NEK1 loss-of-function (LOF) variants were found in individuals with ALS compared to controls. In particular, the p.Arg261His missense variant was associated with significantly increased disease susceptibility. This case series aims to understand the neuropathological phenotypes resulting from NEK1 mutations in ALS. We examined a cohort of three Scottish patients with a mutation in the NEK1 gene and evaluated the distribution and cellular expression of NEK1, as well as the abundance of phosphorylated TDP-43 (pTDP-43) aggregates, in the motor cortex compared to age- and sex-matched control tissue. We show pathological, cytoplasmic TDP-43 aggregates in all three NEK1-ALS cases. NEK1 protein staining revealed no immunoreactivity in two of the NEK1-ALS cases, indicating a LOF and corresponding to a reduction in NEK1 mRNA as detected by in situ hybridisation. However, the p.Arg261His missense mutation resulted in an increase in NEK1 mRNA molecules and abundant NEK1-positive cytoplasmic aggregates, with the same morphologic appearance, and within the same cells as co-occurring TDP-43 aggregates. Here we show the first neuropathological assessment of a series of ALS cases carrying mutations in the NEK1 gene. Specifically, we show that TDP-43 pathology is present in these cases and that potential NEK1 LOF can either be mediated through loss of NEK1 translation or through aggregation of NEK1 protein as in the case with p.Arg261His mutation, a potential novel pathological feature of NEK1-ALS.

Scrutinizing neurodegenerative diseases: decoding the complex genetic architectures through a multi-omics lens

Neurodegenerative diseases present complex genetic architectures, reflecting a continuum from monogenic to oligogenic and polygenic models. Recent advances in multi-omics data, coupled with systems genetics, have significantly refined our understanding of how these data impact neurodegenerative disease mechanisms. To contextualize these genetic discoveries, we provide a comprehensive critical overview of genetic architecture concepts, from Mendelian inheritance to the latest insights from oligogenic and omnigenic models. We explore the roles of common and rare genetic variants, gene-gene and gene-environment interactions, and epigenetic influences in shaping disease phenotypes. Additionally, we emphasize the importance of multi-omics layers including genomic, transcriptomic, proteomic, epigenetic, and metabolomic data in elucidating the molecular mechanisms underlying neurodegeneration. Special attention is given to missing heritability and the contribution of rare variants, particularly in the context of pleiotropy and network pleiotropy. We examine the application of single-cell omics technologies, transcriptome-wide association studies, and epigenome-wide association studies as key approaches for dissecting disease mechanisms at tissue- and cell-type levels. Our review introduces the OmicPeak Disease Trajectory Model, a conceptual framework for understanding the genetic architecture of neurodegenerative disease progression, which integrates multi-omics data across biological layers and time points. This review highlights the critical importance of adopting a systems genetics approach to unravel the complex genetic architecture of neurodegenerative diseases. Finally, this emerging holistic understanding of multi-omics data and the exploration of the intricate genetic landscape aim to provide a foundation for establishing more refined genetic architectures of these diseases, enhancing diagnostic precision, predicting disease progression, elucidating pathogenic mechanisms, and refining therapeutic strategies for neurodegenerative conditions.

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.

The Search for a Universal Treatment for Defined and Mixed Pathology Neurodegenerative Diseases

The predominant neurodegenerative diseases, Alzheimer's disease, Parkinson's disease, dementia with Lewy Bodies, Huntington's disease, amyotrophic lateral sclerosis, and frontotemporal dementia, are rarely pure diseases but, instead, show a diversity of mixed pathologies. At some level, all of them share a combination of one or more different toxic biomarker proteins: amyloid beta (Aβ), phosphorylated Tau (pTau), alpha-synuclein (αSyn), mutant huntingtin (mHtt), fused in sarcoma, superoxide dismutase 1, and TAR DNA-binding protein 43. These toxic proteins share some common attributes, making them potentially universal and simultaneous targets for therapeutic intervention. First, they all form toxic aggregates prior to taking on their final forms as contributors to plaques, neurofibrillary tangles, Lewy bodies, and other protein deposits. Second, the primary enzyme that directs their aggregation is transglutaminase 2 (TGM2), a brain-localized enzyme involved in neurodegeneration. Third, TGM2 binds to calmodulin, a regulatory event that can increase the activity of this enzyme threefold. Fourth, the most common mixed pathology toxic biomarkers (Aβ, pTau, αSyn, nHtt) also bind calmodulin, which can affect their ability to aggregate. This review examines the potential therapeutic routes opened up by this knowledge. The end goal reveals multiple opportunities that are immediately available for universal therapeutic treatment of the most devastating neurodegenerative diseases facing humankind.

Early disruption of the CREB pathway drives dendritic morphological alterations in FTD/ALS cortical neurons

Synaptic loss and dendritic degeneration are common pathologies in several neurodegenerative diseases characterized by progressive cognitive and/or motor decline, such as Alzheimer's disease (AD) and frontotemporal dementia/amyotrophic lateral sclerosis (FTD/ALS). An essential regulator of neuronal health, the cAMP-dependent transcription factor CREB positively regulates synaptic growth, learning, and memory. Phosphorylation of CREB by protein kinase A (PKA) and other cellular kinases promotes neuronal survival and maturation via transcriptional activation of a wide range of downstream target genes. CREB pathway dysfunction has been strongly implicated in AD pathogenesis, and recent data suggest that impaired CREB activation may contribute to disease phenotypes in FTD/ALS as well. However, the mechanisms behind reduced CREB activity in FTD/ALS pathology are not clear. In this study, we found that cortical-like neurons derived from iPSC lines carrying the hexanucleotide repeat expansion in the C9ORF72 gene, a common genetic cause of FTD/ALS, displayed a diminished activation of CREB, resulting in decreased dendritic and synaptic health. Importantly, we determined such impairments to be mechanistically linked to an imbalance in the ratio of regulatory and catalytic subunits of the CREB activator PKA and to be conserved in C9-ALS patient's postmortem tissue. Modulation of cAMP upstream of this impairment allowed for a rescue of CREB activity and an amelioration of dendritic morphology and synaptic protein levels. Our data elucidate the mechanism behind early CREB pathway dysfunction and discern a feasible therapeutic target for the treatment of FTD/ALS and possibly other neurodegenerative diseases.

Opportunities and challenges with G-quadruplexes as promising targets for drug design

INTRODUCTION

G-quadruplexes (G4s) are secondary structures formed in guanine-rich regions of nucleic acids (both DNA and RNA). G4s are significantly enriched at regulatory genomic regions and are associated with important biological processes ranging from telomere homeostasis and genome instability to transcription and translation. Importantly, G4s are related to health and diseases such as cancer, neurological diseases, as well as infections with viruses and microbial pathogens. Increasing evidence suggests the potential of G4s for designing new diagnostic and therapeutic strategies although in vivo studies are still at early stages.

AREAS COVERED

This review provides an updated summary of the literature describing the impact of G4s in human diseases and different approaches based on G4 targeting in therapy.

EXPERT OPINION

Within the G4 field, most of the studies have been performed in vitro and in a descriptive manner. Therefore, detailed mechanistic understanding of G4s in the biological context remains to be deciphered. In clinics, the use of G4s as therapeutic targets has been hindered due to the low selectivity profile and poor drug-like properties of G4 ligands. Future research on G4s may overcome current methodological and interventional limitations and shed light on these unique structural elements in the pathogenesis and treatment of diseases.

Distinct fingerprints of tRNA-derived small non-coding RNA in animal models of neurodegeneration

Transfer RNA-derived small RNAs (tsRNAs) - categorized as tRNA-derived fragments (tRFs), tRNA-derived stress-induced RNAs (tiRNAs) and internal tRF (itRF) - are small non-coding RNAs that participate in various cellular processes such as translation inhibition and responses to cellular stress. We here identified tsRNA profiles within susceptible tissues in animal models of amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD) and Parkinson's disease (PD) to pinpoint disease-specific tsRNAs and those shared across neurodegenerative diseases. We performed small RNA sequencing in the SOD1G93A and TDP43A315T mouse models of ALS (spinal cord), the TauP301S model of FTD (hippocampus), and the parkin/POLG model of PD (substantia nigra). Bioinformatic analysis showed higher expression of 5' tiRNAs selectively in the two ALS models, lower expression of 3' tRFs in both the ALS and FTD mouse models, and lower expression of itRF Arg in the PD model. Experimental validation confirmed the expression of tsRNAs. Gene Ontology analysis of targets associated with validated 3' tRFs indicated functions in the regulation of synaptic and neuronal pathways. Our profiling of tsRNAs indicates disease-specific fingerprints in animal models of neurodegeneration, which require validation in human disease.

An Uncommon Overlap Syndrome Between Ankylosing Spondylitis and Amyotrophic Lateral Sclerosis-Case Report

This case report describes an uncommon overlap syndrome between ankylosing spondylitis (AS) and amyotrophic lateral sclerosis (ALS). Initially, the patient was diagnosed with AS, for which he received various specific treatments, including TNF-α inhibitors. After five years of treatment with TNF-α inhibitor etanercept, the patient was referred for a full neurological assessment after he reported balance disturbances, postural instability, muscle weakness, and other neurological symptoms that indicated the presence of a neurological disorder. After a thorough investigation, the patient was diagnosed with ALS. This case report aims to contribute to the limited literature by providing a detailed case study regarding the crosstalk between AS and ALS while also exploring the potential underlying mechanisms and the possible link between TNF-α inhibitors therapy and ALS.

Apolipoproteins, lipids, lipid-lowering drugs and risk of amyotrophic lateral sclerosis and frontotemporal dementia: a meta-analysis and Mendelian randomisation study

BACKGROUND

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) have clinical, pathological and genetic overlapping. Lipid pathways are implicated in ALS. This study examined the effect of blood lipid levels on ALS, FTD risk, and survival in ALS.

METHODS

A systematic review and meta-analysis of high and low-density lipoprotein cholesterol (HDL-c and LDL-c), total cholesterol, triglycerides, apolipoproteins B and A1 levels with ALS was performed. Two-sample Mendelian randomisation (MR) analysis sought the causal effects of these exposures on ALS, FTD, and survival in ALS. The effect of lipid-lowering drugs was also examined using genetic proxies for targets of lipid-lowering medications.

RESULTS

Three cohort studies met the inclusion criteria for meta-analysis. Meta-analysis indicated an association between higher LDL-c (HRper mmol/L = 1.07, 95%CI:1.02-1.12;I 2 =18%) and lower HDL-c (HRper mmol/L = 0.83, 95%CI:0.74-0.94;I 2 =0%) with an increased risk of ALS. MR suggested causal effects of higher LDL-c (ORIVW = 1.085, 95%:CI 1.008-1.168, pFDR = 0.0406), total cholesterol (ORIVW = 1.081, 95%:CI 1.013-1.154, pFDR = 0.0458) and apolipoprotein B (ORIVW = 1.104, 95%:CI 1.041-1.171, pFDR = 0.0061) increasing ALS risk, and higher apolipoprotein B level increasing FTD risk (ORIVW = 1.424, 95%CI 1.072-1.829, pFDR = 0.0382). Reducing LDL-c through APOB inhibition was associated with lower ALS (ORIVW = 0.84, 95%CI 0.759-0.929, pFDR = 0.00275) and FTD risk (ORIVW = 0.581, 95%CI 0.387-0.874, pFDR = 0.0362).

CONCLUSION

These data support the influence of LDL-c and total cholesterol on ALS risk and apolipoprotein B on the risk of ALS and FTD. Potential APOB inhibition might decrease the risk of sporadic ALS and FTD. Further work in monogenic forms of ALS and FTD is necessary to determine whether blood lipids influence penetrance and phenotype.

Multi-omics analysis using antibody-based in situ biotinylation technique suggests the mechanism of Cajal body formation

Membrane-less subcellular compartments play important roles in various cellular functions. Although techniques exist to identify components of cellular bodies, a comprehensive method for analyzing both static and dynamic states has not been established. Here, we apply an antibody-based in situ biotinylation proximity-labeling technique to identify components of static and dynamic nuclear bodies. Using this approach, we comprehensively identify DNA, RNA, and protein components of Cajal bodies (CBs) and then clarify their interactome. By inhibiting transcription, we capture dynamic changes in CBs. Our analysis reveals that nascent small nuclear RNAs (snRNAs) transcribed in CBs contribute to CB formation by assembling RNA-binding proteins, including frontotemporal dementia-related proteins, RNA-binding motif proteins, and heterogeneous nuclear ribonucleoproteins.

The epigenetic modification of DNA methylation in neurological diseases

Methylation, a key epigenetic modification, is essential for regulating gene expression and protein function without altering the DNA sequence, contributing to various biological processes, including gene transcription, embryonic development, and cellular functions. Methylation encompasses DNA methylation, RNA methylation and histone modification. Recent research indicates that DNA methylation is vital for establishing and maintaining normal brain functions by modulating the high-order structure of DNA. Alterations in the patterns of DNA methylation can exert significant impacts on both gene expression and cellular function, playing a role in the development of numerous diseases, such as neurological disorders, cardiovascular diseases as well as cancer. Our current understanding of the etiology of neurological diseases emphasizes a multifaceted process that includes neurodegenerative, neuroinflammatory, and neurovascular events. Epigenetic modifications, especially DNA methylation, are fundamental in the control of gene expression and are critical in the onset and progression of neurological disorders. Furthermore, we comprehensively overview the role and mechanism of DNA methylation in in various biological processes and gene regulation in neurological diseases. Understanding the mechanisms and dynamics of DNA methylation in neural development can provide valuable insights into human biology and potentially lead to novel therapies for various neurological diseases.

Beyond the usual suspects: multi-factorial computational models in the search for neurodegenerative disease mechanisms

From Alzheimer's disease to amyotrophic lateral sclerosis, the molecular cascades underlying neurodegenerative disorders remain poorly understood. The clinical view of neurodegeneration is confounded by symptomatic heterogeneity and mixed pathology in almost every patient. While the underlying physiological alterations originate, proliferate, and propagate potentially decades before symptomatic onset, the complexity and inaccessibility of the living brain limit direct observation over a patient's lifespan. Consequently, there is a critical need for robust computational methods to support the search for causal mechanisms of neurodegeneration by distinguishing pathogenic processes from consequential alterations, and inter-individual variability from intra-individual progression. Recently, promising advances have been made by data-driven spatiotemporal modeling of the brain, based on in vivo neuroimaging and biospecimen markers. These methods include disease progression models comparing the temporal evolution of various biomarkers, causal models linking interacting biological processes, network propagation models reproducing the spatial spreading of pathology, and biophysical models spanning cellular- to network-scale phenomena. In this review, we discuss various computational approaches for integrating cross-sectional, longitudinal, and multi-modal data, primarily from large observational neuroimaging studies, to understand (i) the temporal ordering of physiological alterations, i(i) their spatial relationships to the brain's molecular and cellular architecture, (iii) mechanistic interactions between biological processes, and (iv) the macroscopic effects of microscopic factors. We consider the extents to which computational models can evaluate mechanistic hypotheses, explore applications such as improving treatment selection, and discuss how model-informed insights can lay the groundwork for a pathobiological redefinition of neurodegenerative disorders.

Histone post-translational modification and heterochromatin alterations in neurodegeneration: revealing novel disease pathways and potential therapeutics

Alzheimer's disease (AD), Parkinson's disease (PD), Frontotemporal Dementia (FTD), and Amyotrophic lateral sclerosis (ALS) are complex and fatal neurodegenerative diseases. While current treatments for these diseases do alleviate some symptoms, there is an imperative need for novel treatments able to stop their progression. For all of these ailments, most cases occur sporadically and have no known genetic cause. Only a small percentage of patients bear known mutations which occur in a multitude of genes. Hence, it is clear that genetic factors alone do not explain disease occurrence. Chromatin, a DNA-histone complex whose basic unit is the nucleosome, is divided into euchromatin, an open form accessible to the transcriptional machinery, and heterochromatin, which is closed and transcriptionally inactive. Protruding out of the nucleosome, histone tails undergo post-translational modifications (PTMs) including methylation, acetylation, and phosphorylation which occur at specific residues and are connected to different chromatin structural states and regulate access to transcriptional machinery. Epigenetic mechanisms, including histone PTMs and changes in chromatin structure, could help explain neurodegenerative disease processes and illuminate novel treatment targets. Recent research has revealed that changes in histone PTMs and heterochromatin loss or gain are connected to neurodegeneration. Here, we review evidence for epigenetic changes occurring in AD, PD, and FTD/ALS. We focus specifically on alterations in the histone PTMs landscape, changes in the expression of histone modifying enzymes and chromatin remodelers as well as the consequences of these changes in heterochromatin structure. We also highlight the potential for epigenetic therapies in neurodegenerative disease treatment. Given their reversibility and pharmacological accessibility, epigenetic mechanisms provide a promising avenue for novel treatments. Altogether, these findings underscore the need for thorough characterization of epigenetic mechanisms and chromatin structure in neurodegeneration.

TDP-43 proteinopathy in frontotemporal lobar degeneration and amyotrophic lateral sclerosis: From pathomechanisms to therapeutic strategies

Proteostasis failure is a common pathological characteristic in neurodegenerative diseases. Revitalizing clearance systems could effectively mitigate these diseases. The transactivation response (TAR) DNA-binding protein 43 (TDP-43) plays a critical role as an RNA/DNA-binding protein in RNA metabolism and synaptic function. Accumulation of TDP-43 aggregates in the central nervous system is a hallmark of frontotemporal lobar degeneration (FTLD) and amyotrophic lateral sclerosis (ALS). Autophagy, a major and highly conserved degradation pathway, holds the potential for degrading aggregated TDP-43 and alleviating FTLD/ALS. This review explores the causes of TDP-43 aggregation, FTLD/ALS-related genes, key autophagy factors, and autophagy-based therapeutic strategies targeting TDP-43 proteinopathy. Understanding the underlying pathological mechanisms of TDP-43 proteinopathy can facilitate therapeutic interventions.

Nucleic Acid Delivery Nanotechnologies for In Vivo Cell Programming

In medicine, it is desirable for clinicians to be able to restore function and imbue novel function into selected cells for therapy and disease prevention. Cells damaged by disease, injury, or aging could be programmed to restore normal or lost functions, such as retinal cells in inherited blindness and neuronal cells in Alzheimer's disease. Cells could also be genetically programmed with novel functions such as immune cells expressing synthetic chimeric antigen receptors for immunotherapy. Furthermore, knockdown or modification of risk factor proteins can mitigate disease development. Currently, nucleic acids are emerging as a versatile and potent therapeutic modality for achieving this cellular programming. In this review, we highlight the latest developments in nanobiomaterials-based nucleic acid therapeutics for cellular programming from a biomaterial design and delivery perspective and how to overcome barriers to their clinical translation to benefit patients.

Ataxin-2: a powerful RNA-binding protein

Ataxin-2 (ATXN2) was originally discovered in the context of spinocerebellar ataxia type 2 (SCA2), but it has become a key player in various neurodegenerative diseases. This review delves into the multifaceted roles of ATXN2 in human diseases, revealing its diverse molecular and cellular pathways. The impact of ATXN2 on diseases extends beyond functional outcomes; it mainly interacts with various RNA-binding proteins (RBPs) to regulate different stages of post-transcriptional gene expression in diseases. With the progress of research, ATXN2 has also been found to play an important role in the development of various cancers, including breast cancer, gastric cancer, pancreatic cancer, colon cancer, and esophageal cancer. This comprehensive exploration underscores the crucial role of ATXN2 in the pathogenesis of diseases and warrants further investigation by the scientific community. By reviewing the latest discoveries on the regulatory functions of ATXN2 in diseases, this article helps us understand the complex molecular mechanisms of a series of human diseases related to this intriguing protein.

Synaptopathy: presynaptic convergence in frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia and amyotrophic lateral sclerosis are common forms of neurodegenerative disease that share overlapping genetics and pathologies. Crucially, no significantly disease-modifying treatments are available for either disease. Identifying the earliest changes that initiate neuronal dysfunction is important for designing effective intervention therapeutics. The genes mutated in genetic forms of frontotemporal dementia and amyotrophic lateral sclerosis have diverse cellular functions, and multiple disease mechanisms have been proposed for both. Identification of a convergent disease mechanism in frontotemporal dementia and amyotrophic lateral sclerosis would focus research for a targetable pathway, which could potentially effectively treat all forms of frontotemporal dementia and amyotrophic lateral sclerosis (both familial and sporadic). Synaptopathies are diseases resulting from physiological dysfunction of synapses, and define the earliest stages in multiple neuronal diseases, with synapse loss a key feature in dementia. At the presynapse, the process of synaptic vesicle recruitment, fusion and recycling is necessary for activity-dependent neurotransmitter release. The unique distal location of the presynaptic terminal means the tight spatio-temporal control of presynaptic homeostasis is dependent on efficient local protein translation and degradation. Recently, numerous publications have shown that mutations associated with frontotemporal dementia and amyotrophic lateral sclerosis present with synaptopathy characterized by presynaptic dysfunction. This review will describe the complex local signalling and membrane trafficking events that occur at the presynapse to facilitate neurotransmission and will summarize recent publications linking frontotemporal dementia/amyotrophic lateral sclerosis genetic mutations to presynaptic function. This evidence indicates that presynaptic synaptopathy is an early and convergent event in frontotemporal dementia and amyotrophic lateral sclerosis and illustrates the need for further research in this area, to identify potential therapeutic targets with the ability to impact this convergent pathomechanism.

Long way up: rethink diseases in light of phase separation and phase transition

Biomolecular condensation, driven by multivalency, serves as a fundamental mechanism within cells, facilitating the formation of distinct compartments, including membraneless organelles that play essential roles in various cellular processes. Perturbations in the delicate equilibrium of condensation, whether resulting in gain or loss of phase separation, have robustly been associated with cellular dysfunction and physiological disorders. As ongoing research endeavors wholeheartedly embrace this newly acknowledged principle, a transformative shift is occurring in our comprehension of disease. Consequently, significant strides have been made in unraveling the profound relevance and potential causal connections between abnormal phase separation and various diseases. This comprehensive review presents compelling recent evidence that highlight the intricate associations between aberrant phase separation and neurodegenerative diseases, cancers, and infectious diseases. Additionally, we provide a succinct summary of current efforts and propose innovative solutions for the development of potential therapeutics to combat the pathological consequences attributed to aberrant phase separation.

Mendelian Randomization Identifies Genetically Supported Drug Targets for Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Currently, amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) have no effective treatments. Drug repurposing offers a rapid method to meet therapeutic need for ALS and FTD. To identify therapeutic targets associated with ALS and FTD, Mendelian randomization (MR) analysis and colocalization were performed. Genetic instruments were based on transcriptomic and proteomic data for 422 actionable proteins targeted by approved drugs or clinical drug candidates. The publicly available ALS GWAS summary data (including a total of 20,806 ALS cases and 59,804 controls) and FTD GWAS summary data (including a total of 2154 patients with FTD and 4308 controls) were used. Using cis-expression quantitative trait loci and cis-protein quantitative trait loci genetic instruments, we identified several drug targets for repurposing (ALS: MARK3, false-discovery rate (FDR) = 0.043; LTBR, FDR = 0.068) (FTD: HLA-DRB1, FDR = 0.083; ADH5, FDR = 0.056). Our MR study analyzed the actionable druggable proteins and provided potential therapeutic targets for ALS and FTD. Future studies should further elucidate the underlying mechanism of corresponding drug targets in the pathogenesis of ALS and FTD.

Unraveling the multifaceted insights into amyotrophic lateral sclerosis: Genetic underpinnings, pathogenesis, and therapeutic horizons

Amyotrophic Lateral Sclerosis (ALS), a progressive neurodegenerative disease, primarily impairs upper and lower motor neurons, leading to debilitating motor dysfunction and eventually respiratory failure, widely known as Lou Gehrig's disease. ALS presents with diverse symptomatology, including dysarthria, dysphagia, muscle atrophy, and hyperreflexia. The prevalence of ALS varies globally, with incidence rates ranging from 1.5 to 3.8 per 100,000 individuals, significantly affecting populations aged 45-80. A complex interplay of genetic and environmental factors underpins ALS pathogenesis. Key genetic contributors include mutations in chromosome 9 open reading frame 72 (C9ORF72), superoxide dismutase type 1 (SOD1), Fusedin sarcoma (FUS), and TAR DNA-binding protein (TARDBP) genes, accounting for a considerable fraction of both familial (fALS) and sporadic (sALS) cases. The disease mechanism encompasses aberrant protein folding, mitochondrial dysfunction, oxidative stress, excitotoxicity, and neuroinflammation, contributing to neuronal death. This review consolidates current insights into ALS's multifaceted etiology, highlighting the roles of environmental exposures (e.g., toxins, heavy metals) and their interaction with genetic predispositions. We emphasize the polygenic nature of ALS, where multiple genetic variations cumulatively influence disease susceptibility and progression. This aspect underscores the challenges in ALS diagnosis, which currently lacks specific biomarkers and relies on symptomatology and familial history. Therapeutic strategies for ALS, still in nascent stages, involve symptomatic management and experimental approaches targeting molecular pathways implicated in ALS pathology. Gene therapy, focusing on specific ALS mutations, and stem cell therapy emerge as promising avenues. However, effective treatments remain elusive, necessitating a deeper understanding of ALS's genetic architecture and the development of targeted therapies based on personalized medicine principles. This review aims to provide a comprehensive understanding of ALS, encouraging further research into its complex genetic underpinnings and the development of innovative, effective treatment modalities.

Plasma extracellular vesicle tau and TDP-43 as diagnostic biomarkers in FTD and ALS

Minimally invasive biomarkers are urgently needed to detect molecular pathology in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Here, we show that plasma extracellular vesicles (EVs) contain quantifiable amounts of TDP-43 and full-length tau, which allow the quantification of 3-repeat (3R) and 4-repeat (4R) tau isoforms. Plasma EV TDP-43 levels and EV 3R/4R tau ratios were determined in a cohort of 704 patients, including 37 genetically and 31 neuropathologically proven cases. Diagnostic groups comprised patients with TDP-43 proteinopathy ALS, 4R tauopathy progressive supranuclear palsy, behavior variant FTD (bvFTD) as a group with either tau or TDP-43 pathology, and healthy controls. EV tau ratios were low in progressive supranuclear palsy and high in bvFTD with tau pathology. EV TDP-43 levels were high in ALS and in bvFTD with TDP-43 pathology. Both markers discriminated between the diagnostic groups with area under the curve values >0.9, and between TDP-43 and tau pathology in bvFTD. Both markers strongly correlated with neurodegeneration, and clinical and neuropsychological markers of disease severity. Findings were replicated in an independent validation cohort of 292 patients including 34 genetically confirmed cases. Taken together, the combination of EV TDP-43 levels and EV 3R/4R tau ratios may aid the molecular diagnosis of FTD, FTD spectrum disorders and ALS, providing a potential biomarker to monitor disease progression and target engagement in clinical trials.

Systematic review and meta-analysis of dysregulated microRNAs derived from liquid biopsies as biomarkers for amyotrophic lateral sclerosis

The discovery of disease-specific biomarkers, such as microRNAs (miRNAs), holds the potential to transform the landscape of Amyotrophic Lateral Sclerosis (ALS) by facilitating timely diagnosis, monitoring treatment response, and accelerating drug discovery. Such advancement could ultimately improve the quality of life and survival rates for ALS patients. Despite more than a decade of research, no miRNA biomarker candidate has been translated into clinical practice. We conducted a systematic review and meta-analysis to quantitatively synthesize data from original studies that analyzed miRNA expression from liquid biopsies via PCR and compared them to healthy controls. Our analysis encompasses 807 miRNA observations from 31 studies, stratified according to their source tissue. We identified consistently dysregulated miRNAs in serum (hsa-miR-3665, -4530, -4745-5p, -206); blood (hsa-miR-338-3p, -183-5p); cerebrospinal fluid (hsa-miR-34a-3p); plasma (hsa-miR-206); and neural-enriched extracellular vesicles from plasma (hsa-miR-146a-5p, -151a-5p, -10b-5p, -29b-3p, and -4454). The meta-analyses provided further support for the upregulation of hsa-miR-206, hsa-miR-338-3p, hsa-miR-146a-5p and hsa-miR-151a-5p, and downregulation of hsa-miR-183-5p, hsa-miR-10b-5p, hsa-miR-29b-3p, and hsa-miR-4454 as consistent indicators of ALS across independent studies. Our findings provide valuable insights into the current understanding of miRNAs' dysregulated expression in ALS patients and on the researchers' choices of methodology. This work contributes to the ongoing efforts towards discovering disease-specific biomarkers.

Cognitive function in amyotrophic lateral sclerosis: a cross-sectional and prospective pragmatic clinical study with review of the literature

BACKGROUND

Amyotrophic lateral sclerosis (ALS) can present with either bulbar or spinal symptoms, and in some cases, both types of symptoms may be present. In addition, cognitive impairment has been observed in ALS. The study aimed to evaluate the frontal and general cognitive performance in ALS not only cross-sectionally but also longitudinally.

METHODS AND MATERIALS

The Frontal Assessment Battery (FAB) and the Montreal Cognitive Assessment (MoCA) were employed to assess cognitive function in 52 adults with ALS and 52 cognitively healthy individuals. The statistical analyses encompassed the Pearson Chi square test, the Skillings-Mack test, the Spearman's rank correlation coefficient, and the Proportional Odds Logistic Regression Model (POLR).

RESULTS

Cross-sectionally, lower cognitive performance was associated with ALS diagnosis, older age, and motor functional decline. The cognitive impairment of individuals with bulbar and spinal-bulbar symptoms showed faster deterioration compared to those with spinal symptoms. The spinal subgroup consistently performed worst in delayed recall and attention, while the spinal-bulbar and bulbar subgroups exhibited inferior scores in delayed recall, attention, visuospatial skills, orientation, and verbal fluency.

CONCLUSION

The incorporation of cognitive screening in the diagnostic workup of ALS may be beneficial, as early detection can enhance symptom management and improve the quality of life for both individuals with ALS and their care partners.

Single-cell dissection of the human motor and prefrontal cortices in ALS and FTLD

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) share many clinical, pathological, and genetic features, but a detailed understanding of their associated transcriptional alterations across vulnerable cortical cell types is lacking. Here, we report a high-resolution, comparative single-cell molecular atlas of the human primary motor and dorsolateral prefrontal cortices and their transcriptional alterations in sporadic and familial ALS and FTLD. By integrating transcriptional and genetic information, we identify known and previously unidentified vulnerable populations in cortical layer 5 and show that ALS- and FTLD-implicated motor and spindle neurons possess a virtually indistinguishable molecular identity. We implicate potential disease mechanisms affecting these cell types as well as non-neuronal drivers of pathogenesis. Finally, we show that neuron loss in cortical layer 5 tracks more closely with transcriptional identity rather than cellular morphology and extends beyond previously reported vulnerable cell types.

Genetics screening in an Italian cohort of patients with Amyotrophic Lateral Sclerosis: the importance of early testing and its implication

INTRODUCTION

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease with an elusive etiology. While environmental factors have been considered, familial ALS cases have raised the possibility of genetic involvement. This genetic connection is increasingly evident, even in patients with sporadic ALS. We allowed access to the genetic test to all patients attending our clinic to identify the prevalence and the role of genetic variants in the development of the disease and to identify patients with potentially treatable forms of the disease.

MATERIALS AND METHODS

194 patients with probable or definite ALS, were enrolled. A comprehensive genetic testing was performed, including sequencing all exons of the SOD1 gene and testing for hexanucleotide intronic repeat expansions (G4C2) in the C9orf72 gene using fluorescent repeat-primed PCR (RP-PCR). Whole Exome NGS Sequencing (WES) was performed, followed by an in silico multigene panel targeting neuromuscular diseases, spastic paraplegia, and motor distal neuropathies. We conducted statistical analyses to compare different patient groups.

RESULTS

Clinically significant pathogenetic variants were detected in 14.43% of cases. The highest prevalence of pathogenetic variants was observed in fALS patients, but a substantial proportion of sALS patients also displayed at least one variant, either pathogenetic or of uncertain significance (VUS). The most observed pathogenetic variant was the expansion of the C9orf72 gene, which was associated with a shorter survival. SOD1 variants were found in 1.6% of fALS and 2.5% of sALS patients.

DISCUSSION

The study reveals a significant number of ALS patients carrying pathogenic or likely pathogenic variants, with a higher prevalence in familial ALS cases. The expansion of the C9orf72 gene emerges as the most common genetic cause of ALS, affecting familial and sporadic cases. Additionally, SOD1 variants are detected at an unexpectedly higher rate, even in patients without a familial history of ALS, underscoring the crucial role of genetic testing in treatment decisions and potential participation in clinical trials. We also investigated variants in genes such as TARDBP, FUS, NEK1, TBK1, and DNAJC7, shedding light on their potential involvement in ALS. These findings underscore the complexity of interpreting variants of uncertain significance (VUS) and their ethical implications in patient communication and genetic counseling for patients' relatives.

CONCLUSION

This study emphasizes the diverse genetic basis of ALS and advocates for integrating comprehensive genetic testing into diagnostic protocols. The evolving landscape of genetic therapies requires identifying all eligible patients transcending traditional familial boundaries. The presence of VUS highlights the multifaceted nature of ALS genetics, prompting further exploration of complex interactions among genetic variants, environmental factors, and disease development.

Oligodendrocytes in amyotrophic lateral sclerosis and frontotemporal dementia: the new players on stage

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are fatal adult-onset neurodegenerative disorders that share clinical, neuropathological and genetic features, which forms part of a multi-system disease spectrum. The pathological process leading to ALS and FTD is the result of the combination of multiple mechanisms that operate within specific populations of neurons and glial cells. The implication of oligodendrocytes has been the subject of a number of studies conducted on patients and related animal models. In this review we summarize our current knowledge on the alterations specific to myelin and the oligodendrocyte lineage occurring in ALS and FTD. We also consider different ways by which specific oligodendroglial alterations influence neurodegeneration and highlight the important role of oligodendrocytes in these two intrinsically associated neurodegenerative diseases.

The implications of physiological biomolecular condensates in amyotrophic lateral sclerosis

In recent years, there has been an emphasis on the role of phase-separated biomolecular condensates, especially stress granules, in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). This is largely due to several ALS-associated mutations occurring in genes involved in stress granule assembly and observations that pathological inclusions detected in ALS patient neurons contain stress granule proteins, including the ALS-linked proteins TDP-43 and FUS. However, protein components of stress granules are also found in numerous other phase-separated biomolecular condensates under physiological conditions which are inadequately discussed in the context of ALS. In this review, we look beyond stress granules and describe the roles of TDP-43 and FUS in physiological condensates occurring in the nucleus and neurites, such as the nucleolus, Cajal bodies, paraspeckles and neuronal RNA transport granules. We also discuss the consequences of ALS-linked mutations in TDP-43 and FUS on their ability to phase separate into these stress-independent biomolecular condensates and perform their respective functions. Importantly, biomolecular condensates sequester multiple overlapping protein and RNA components, and their dysregulation could contribute to the observed pleiotropic effects of both sporadic and familial ALS on RNA metabolism.

C9orf72 gene networks in the human brain correlate with cortical thickness in C9-FTD and implicate vulnerable cell types

Introduction

A hexanucleotide repeat expansion (HRE) intronic to chromosome 9 open reading frame 72 (C9orf72) is recognized as the most common genetic cause of amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and ALS-FTD. Identifying genes that show similar regional co-expression patterns to C9orf72 may help identify novel gene targets and biological mechanisms that mediate selective vulnerability to ALS and FTD pathogenesis.

Methods

We leveraged mRNA expression data in healthy brain from the Allen Human Brain Atlas to evaluate C9orf72 co-expression patterns. To do this, we correlated average C9orf72 expression values in 51 regions across different anatomical divisions (cortex, subcortex, and cerebellum) with average gene expression values for 15,633 protein-coding genes, including 54 genes known to be associated with ALS, FTD, or ALS-FTD. We then performed imaging transcriptomic analyses to evaluate whether the identified C9orf72 co-expressed genes correlated with patterns of cortical thickness in symptomatic C9orf72 pathogenic HRE carriers (n = 19) compared to controls (n = 23). Lastly, we explored whether genes with significant C9orf72 imaging transcriptomic correlations (i.e., "C9orf72 imaging transcriptomic network") were enriched in specific cell populations in the brain and enriched for specific biological and molecular pathways.

Results

A total of 2,120 genes showed an anatomical distribution of gene expression in the brain similar to C9orf72 and significantly correlated with patterns of cortical thickness in C9orf72 HRE carriers. This C9orf72 imaging transcriptomic network was differentially expressed in cell populations previously implicated in ALS and FTD, including layer 5b cells, cholinergic neurons in the spinal cord and brainstem and medium spiny neurons of the striatum, and was enriched for biological and molecular pathways associated with protein ubiquitination, autophagy, cellular response to DNA damage, endoplasmic reticulum to Golgi vesicle-mediated transport, among others.

Conclusion

Considered together, we identified a network of C9orf72 associated genes that may influence selective regional and cell-type-specific vulnerabilities in ALS/FTD.

Counter-regulation of RNA stability by UPF1 and TDP43

RNA quality control is crucial for proper regulation of gene expression. Disruption of nonsense mediated mRNA decay (NMD), the primary RNA decay pathway responsible for the degradation of transcripts containing premature termination codons (PTCs), can disrupt development and lead to multiple diseases in humans and other animals. Similarly, therapies targeting NMD may have applications in hematological, neoplastic and neurological disorders. As such, tools capable of accurately quantifying NMD status could be invaluable for investigations of disease pathogenesis and biomarker identification. Toward this end, we assemble, validate, and apply a next-generation sequencing approach (NMDq) for identifying and measuring the abundance of PTC-containing transcripts. After validating NMDq performance and confirming its utility for tracking RNA surveillance, we apply it to determine pathway activity in two neurodegenerative diseases, amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) characterized by RNA misprocessing and abnormal RNA stability. Despite the genetic and pathologic evidence implicating dysfunctional RNA metabolism, and NMD in particular, in these conditions, we detected no significant differences in PTC-encoding transcripts in ALS models or disease. Contrary to expectations, overexpression of the master NMD regulator UPF1 had little effect on the clearance of transcripts with PTCs, but rather restored RNA homeostasis through differential use and decay of alternatively poly-adenylated isoforms. Together, these data suggest that canonical NMD is not a significant contributor to ALS/FTD pathogenesis, and that UPF1 promotes neuronal survival by regulating transcripts with abnormally long 3'UTRs.

Unraveling the Genetic Landscape of Neurological Disorders: Insights into Pathogenesis, Techniques for Variant Identification, and Therapeutic Approaches

Genetic abnormalities play a crucial role in the development of neurodegenerative disorders (NDDs). Genetic exploration has indeed contributed to unraveling the molecular complexities responsible for the etiology and progression of various NDDs. The intricate nature of rare and common variants in NDDs contributes to a limited understanding of the genetic risk factors associated with them. Advancements in next-generation sequencing have made whole-genome sequencing and whole-exome sequencing possible, allowing the identification of rare variants with substantial effects, and improving the understanding of both Mendelian and complex neurological conditions. The resurgence of gene therapy holds the promise of targeting the etiology of diseases and ensuring a sustained correction. This approach is particularly enticing for neurodegenerative diseases, where traditional pharmacological methods have fallen short. In the context of our exploration of the genetic epidemiology of the three most prevalent NDDs-amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease, our primary goal is to underscore the progress made in the development of next-generation sequencing. This progress aims to enhance our understanding of the disease mechanisms and explore gene-based therapies for NDDs. Throughout this review, we focus on genetic variations, methodologies for their identification, the associated pathophysiology, and the promising potential of gene therapy. Ultimately, our objective is to provide a comprehensive and forward-looking perspective on the emerging research arena of NDDs.

C9orf72-associated dipeptide protein repeats form A11-positive oligomers in amyotrophic lateral sclerosis and frontotemporal dementia

Hexanucleotide repeat expansion in C9orf72 is one of the most common causes of amyotrophic lateral sclerosis and frontotemporal dementia. The hexanucleotide expansion, formed by GGGGCC (G4C2) repeats, leads to the production of five dipeptide protein repeats (DPRs) via repeat-associated non-AUG translation. Among the five dipeptide repeats, Gly-Arg, Pro-Arg, and Gly-Ala form neuronal inclusions that contain aggregates of the peptides. Several studies have attempted to model DPR-associated toxicity using various repeat lengths, which suggests a unique conformation that is cytotoxic and is independent of the repeat length. However, the structural characteristics of DPR aggregates have yet to be determined. Increasing evidence suggests that soluble species, such as oligomers, are the main cause of toxicity in proteinopathies, such as Alzheimer's and Parkinson's disease. To investigate the ability of DPRs to aggregate and form toxic oligomers, we adopted a reductionist approach using small dipeptide repeats of 3, 6, and 12. This study shows that DPRs, particularly glycine-arginine and proline-arginine, form oligomers that exhibit distinct dye-binding properties and morphologies. Importantly, we also identified toxic DPR oligomers in amyotrophic lateral sclerosis and frontotemporal dementia postmortem brains that are morphologically similar to those generated recombinantly. This study demonstrates that, similar to soluble oligomers formed by various amyloid proteins, DPR oligomers are toxic, independent of their repeat length.

ALS' Perfect Storm: C9orf72-Associated Toxic Dipeptide Repeats as Potential Multipotent Disruptors of Protein Homeostasis

Protein homeostasis is essential for neuron longevity, requiring a balanced regulation between protein synthesis and degradation. The clearance of misfolded and aggregated proteins, mediated by autophagy and the ubiquitin-proteasome systems, maintains protein homeostasis in neurons, which are post-mitotic and thus cannot use cell division to diminish the burden of misfolded proteins. When protein clearance pathways are overwhelmed or otherwise disrupted, the accumulation of misfolded or aggregated proteins can lead to the activation of ER stress and the formation of stress granules, which predominantly attempt to restore the homeostasis by suppressing global protein translation. Alterations in these processes have been widely reported among studies investigating the toxic function of dipeptide repeats (DPRs) produced by G4C2 expansion in the C9orf72 gene of patients with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). In this review, we outline the modalities of DPR-induced disruptions in protein homeostasis observed in a wide range of models of C9orf72-linked ALS/FTD. We also discuss the relative importance of each DPR for toxicity, possible synergies between DPRs, and discuss the possible functional relevance of DPR aggregation to disease pathogenesis. Finally, we highlight the interdependencies of the observed effects and reflect on the importance of feedback and feedforward mechanisms in their contribution to disease progression. A better understanding of DPR-associated disease pathogenesis discussed in this review might shed light on disease vulnerabilities that may be amenable with therapeutic interventions.

Pathomechanistic Networks of Motor System Injury in Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is the most common, adult-onset, progressive motor neurodegenerative disorder that results in death within 3 years of the clinical diagnosis. Due to the clinicopathological heterogeneity, any reliable biomarkers for diagnosis or prognosis of ALS have not been identified till date. Moreover, the only three clinically approved treatments are not uniformly effective in slowing the disease progression. Over the last 15 years, there has been a rapid advancement in research on the complex pathomechanistic landscape of ALS that has opened up new avenues for successful clinical translation of targeted therapeutics. Multiple studies suggest that the age-dependent interaction of risk-associated genes with environmental factors and endogenous modifiers is critical to the multi-step process of ALS pathogenesis. In this review, we provide an updated discussion on the dysregulated cross-talk between intracellular homeostasis processes, the unique molecular networks across selectively vulnerable cell types, and the multisystemic nature of ALS pathomechanisms. Importantly, this work highlights the alteration in epigenetic and epitranscriptomic landscape due to gene-environment interactions, which have been largely overlooked in the context of ALS pathology. Finally, we suggest that precision medicine research in ALS will be largely benefitted from the stratification of patient groups based on the clinical phenotype, onset and progression, genome, exposome, and metabolic identities.

Disrupted endoplasmic reticulum-mediated autophagosomal biogenesis in a Drosophila model of C9-ALS-FTD

ABBREVIATIONS

3R: UAS construct expressing 3 G4C2 repeats (used as control); 3WJ: three-way junction; 12R: UAS construct expressing leader sequence and 12 G4C2 repeats; 30R: UAS construct expressing 30 G4C2 repeats; 36R: UAS construct expressing 36 G4C2 repeats; 44R: UAS construct expressing leader sequence and 44 G4C2 repeats; ALS: amyotrophic lateral sclerosis; Atg: autophagy related; atl: atlastin; C9-ALS-FTD: ALS or FTD caused by hexanuleotide repeat expansion in C9orf72; ER: endoplasmic reticulum; FTD: frontotemporal dementia; HRE: GGGGCC hexanucleotide repeat expansion; HSP: hereditary spastic paraplegia; Lamp1: lysosomal associated membrane protein 1; MT: microtubule; NMJ: neuromuscular junction; Rab: Ras-associated binding GTPase; RAN: repeat associated non-AUG (RAN) translation; RO-36: UAS construct expression "RNA-only" version of 36 G4C2 repeats in which stop codons in all six reading frames are inserted.; Rtnl1: Reticulon-like 1; SN: segmental nerve; TFEB/Mitf: transcription factor EB/microphthalmia associated transcription factor (Drosophila ortholog of TFEB); TrpA1: transient receptor potential cation channel A1; VAPB: VAMP associated protein B and C; VNC: ventral nerve cord (spinal cord in Drosophila larvae).

Evaluation of an educational conference for persons affected by hereditary frontotemporal degeneration and amyotrophic lateral sclerosis

Objective

There are limited studies exploring the support and education needs of individuals at-risk for or diagnosed with hereditary frontotemporal degeneration (FTD) and/or amyotrophic lateral sclerosis (ALS). This study evaluated a novel conference for this population to assess conference efficacy, probe how participants assessed relevant resources, and identify outstanding needs of persons at-risk/diagnosed.

Methods

We implemented a post-conference electronic survey that probed participants' satisfaction, prior experience with resources, and unmet needs. Along with multiple-choice, free-text items were included to gather qualitative context.

Results

Survey completion rate was 31% (115/376 attendees who were emailed the survey). There was positive interest in pursuing genetic counseling among eligible responders: 61% indicated they planned to seek genetic counseling because of the conference, which was significantly more than those who were undecided (21%) or did not plan to seek genetic counseling (18%). Qualitative data demonstrated need for additional education, support, and research opportunities.

Conclusion

Conference reactions indicate this is a valued resource. Results indicated the importance of raising awareness about existing resources, and the need for further resource development, especially for at-risk communities.

Innovation

While most resources are developed for caregivers' needs, this unique program targets at-risk individuals and unites ALS and FTD communities.

Protein Biomarkers Shared by Multiple Neurodegenerative Diseases Are Calmodulin-Binding Proteins Offering Novel and Potentially Universal Therapeutic Targets

Seven major neurodegenerative diseases and their variants share many overlapping biomarkers that are calmodulin-binding proteins: Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), frontotemporal lobar dementia (FTD), Huntington's disease (HD), Lewy body disease (LBD), multiple sclerosis (MS), and Parkinson's disease (PD). Calcium dysregulation is an early and persistent event in each of these diseases, with calmodulin serving as an initial and primary target of increased cytosolic calcium. Considering the central role of calcium dysregulation and its downstream impact on calcium signaling, calmodulin has gained interest as a major regulator of neurodegenerative events. Here, we show that calmodulin serves a critical role in neurodegenerative diseases via binding to and regulating an abundance of biomarkers, many of which are involved in multiple neurodegenerative diseases. Of special interest are the shared functions of calmodulin in the generation of protein biomarker aggregates in AD, HD, LBD, and PD, where calmodulin not only binds to amyloid beta, pTau, alpha-synuclein, and mutant huntingtin but also, via its regulation of transglutaminase 2, converts them into toxic protein aggregates. It is suggested that several calmodulin binding proteins could immediately serve as primary drug targets, while combinations of calmodulin binding proteins could provide simultaneous insight into the onset and progression of multiple neurodegenerative diseases.

Inflammasome assembly in neurodegenerative diseases

Neurodegenerative disorders are characterized by the progressive dysfunction and death of selectively vulnerable neuronal populations, often associated with the accumulation of aggregated host proteins. Sustained brain inflammation and hyperactivation of inflammasome complexes have been increasingly demonstrated to contribute to neurodegenerative disease progression. Here, we review molecular mechanisms leading to inflammasome assembly in neurodegeneration. We focus primarily on four degenerative brain disorders in which inflammasome hyperactivation has been well documented: Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), and the spectrum of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). We discuss shared and divergent principles of inflammasome assembly across these disorders, and underscore the differences between neurodegeneration-associated inflammasome activation pathways and their peripheral-immune counterparts. We examine how aberrant assembly of inflammasome complexes may amplify pathology in neurodegeneration, including misfolded protein aggregation, and highlight prospects for neurotherapeutic interventions based on targeting inflammasome pathways.

A toxic gain-of-function mechanism in C9orf72 ALS impairs the autophagy-lysosome pathway in neurons

BACKGROUND

Motor neurons (MNs), which are primarily affected in amyotrophic lateral sclerosis (ALS), are a specialized type of neurons that are long and non-dividing. Given their unique structure, these cells heavily rely on transport of organelles along their axons and the process of autophagy to maintain their cellular homeostasis. It has been shown that disruption of the autophagy pathway is sufficient to cause progressive neurodegeneration and defects in autophagy have been associated with various subtypes of ALS, including those caused by hexanucleotide repeat expansions in the C9orf72 gene. A more comprehensive understanding of the dysfunctional cellular mechanisms will help rationalize the design of potent and selective therapies for C9orf72-ALS.

METHODS

In this study, we used induced pluripotent stem cell (iPSC)-derived MNs from C9orf72-ALS patients and isogenic control lines to identify the underlying mechanisms causing dysregulations of the autophagy-lysosome pathway. Additionally, to ascertain the potential impact of C9orf72 loss-of-function on autophagic defects, we characterized the observed phenotypes in a C9orf72 knockout iPSC line (C9-KO).

RESULTS

Despite the evident presence of dysfunctions in several aspects of the autophagy-lysosome pathway, such as disrupted lysosomal homeostasis, abnormal lysosome morphology, inhibition of autophagic flux, and accumulation of p62 in C9orf72-ALS MNs, we were surprised to find that C9orf72 loss-of-function had minimal influence on these phenotypes. Instead, we primarily observed impairment in endosome maturation as a result of C9orf72 loss-of-function. Additionally, our study shed light on the pathological mechanisms underlying C9orf72-ALS, as we detected an increased TBK1 phosphorylation at S172 in MNs derived from C9orf72 ALS patients.

CONCLUSIONS

Our data provides further insight into the involvement of defects in the autophagy-lysosome pathway in C9orf72-ALS and strongly indicate that those defects are mainly due to the toxic gain-of-function mechanisms underlying C9orf72-ALS.

Divergent single cell transcriptome and epigenome alterations in ALS and FTD patients with C9orf72 mutation

A repeat expansion in the C9orf72 (C9) gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we investigate single nucleus transcriptomics (snRNA-seq) and epigenomics (snATAC-seq) in postmortem motor and frontal cortices from C9-ALS, C9-FTD, and control donors. C9-ALS donors present pervasive alterations of gene expression with concordant changes in chromatin accessibility and histone modifications. The greatest alterations occur in upper and deep layer excitatory neurons, as well as in astrocytes. In neurons, the changes imply an increase in proteostasis, metabolism, and protein expression pathways, alongside a decrease in neuronal function. In astrocytes, the alterations suggest activation and structural remodeling. Conversely, C9-FTD donors have fewer high-quality neuronal nuclei in the frontal cortex and numerous gene expression changes in glial cells. These findings highlight a context-dependent molecular disruption in C9-ALS and C9-FTD, indicating unique effects across cell types, brain regions, and diseases.

Damaged mitochondria recruit the effector NEMO to activate NF-κB signaling

Failure to clear damaged mitochondria via mitophagy disrupts physiological function and may initiate damage signaling via inflammatory cascades, although how these pathways intersect remains unclear. We discovered that nuclear factor kappa B (NF-κB) essential regulator NF-κB effector molecule (NEMO) is recruited to damaged mitochondria in a Parkin-dependent manner in a time course similar to recruitment of the structurally related mitophagy adaptor, optineurin (OPTN). Upon recruitment, NEMO partitions into phase-separated condensates distinct from OPTN but colocalizing with p62/SQSTM1. NEMO recruitment, in turn, recruits the active catalytic inhibitor of kappa B kinase (IKK) component phospho-IKKβ, initiating NF-κB signaling and the upregulation of inflammatory cytokines. Consistent with a potential neuroinflammatory role, NEMO is recruited to mitochondria in primary astrocytes upon oxidative stress. These findings suggest that damaged, ubiquitinated mitochondria serve as an intracellular platform to initiate innate immune signaling, promoting the formation of activated IKK complexes sufficient to activate NF-κB signaling. We propose that mitophagy and NF-κB signaling are initiated as parallel pathways in response to mitochondrial stress.

Amyotrophic lateral sclerosis: translating genetic discoveries into therapies

Recent advances in sequencing technologies and collaborative efforts have led to substantial progress in identifying the genetic causes of amyotrophic lateral sclerosis (ALS). This momentum has, in turn, fostered the development of putative molecular therapies. In this Review, we outline the current genetic knowledge, emphasizing recent discoveries and emerging concepts such as the implication of distinct types of mutation, variability in mutated genes in diverse genetic ancestries and gene-environment interactions. We also propose a high-level model to synthesize the interdependent effects of genetics, environmental and lifestyle factors, and ageing into a unified theory of ALS. Furthermore, we summarize the current status of therapies developed on the basis of genetic knowledge established for ALS over the past 30 years, and we discuss how developing treatments for ALS will advance our understanding of targeting other neurological diseases.