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

Identifying FUS amyotrophic lateral sclerosis disease signatures in patient dermal fibroblasts

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing, highly heterogeneous neurodegenerative disease, underscoring the importance of obtaining information to personalize clinical decisions quickly after diagnosis. Here, we investigated whether ALS-relevant signatures can be detected directly from biopsied patient fibroblasts. We profiled familial ALS (fALS) fibroblasts, representing a range of mutations in the fused in sarcoma (FUS) gene and ages of onset. To differentiate FUS fALS and healthy control fibroblasts, machine-learning classifiers were trained separately on high-content imaging and transcriptional profiles. "Molecular ALS phenotype" scores, derived from these classifiers, captured a spectrum from disease to health. Interestingly, these scores negatively correlated with age of onset, identified several pre-symptomatic individuals and sporadic ALS (sALS) patients with FUS-like fibroblasts, and quantified "movement" of FUS fALS and "FUS-like" sALS toward health upon FUS ASO treatment. Taken together, these findings provide evidence that non-neuronal patient fibroblasts can be used for rapid, personalized assessment in ALS.

Structural basis for RNA recognition by the C-terminal RRM domain of human RBM45

RBM45 is an RNA-binding protein with roles in neural development by regulating RNA splicing. Its dysfunction and aggregation are associated with neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal lobar dementia (FTLD). RBM45 harbors three RRM domains that potentially bind RNA. While the recognitions of RNA by its N-terminal tandem RRM domains (RRM1 and RRM2) have been well understood, the RNA-binding property of its C-terminal RRM (RRM3) remains unclear. In this work, we identified that the RRM3 of RBM45 sequence-specifically binds RNA with a GACG sequence, similar but not identical to those recognized by the RRM1 and RRM2. Further, we determined the crystal structure of RBM45RRM3 in complex with a GACG sequence-containing single-stranded DNA. Our structural results, together with the RNA-binding assays of mutants at key amino acid residues, revealed the molecular mechanism by which RBM45RRM3 recognizes an RNA sequence. Our finding on the RNA-binding property of the individual RRM module of RBM45 provides the foundation for unraveling the RNA-binding characteristics of full-length RBM45 and for understanding the biological functions of RBM45.

Excessive STAU1 condensate drives mTOR translation and autophagy dysfunction in neurodegeneration

The double-stranded RNA-binding protein Staufen1 (STAU1) regulates a variety of physiological and pathological events via mediating RNA metabolism. STAU1 overabundance was observed in tissues from mouse models and fibroblasts from patients with neurodegenerative diseases, accompanied by enhanced mTOR signaling and impaired autophagic flux, while the underlying mechanism remains elusive. Here, we find that endogenous STAU1 forms dynamic cytoplasmic condensate in normal and tumor cell lines, as well as in mouse Huntington's disease knockin striatal cells. STAU1 condensate recruits target mRNA MTOR at its 5'UTR and promotes its translation both in vitro and in vivo, and thus enhanced formation of STAU1 condensate leads to mTOR hyperactivation and autophagy-lysosome dysfunction. Interference of STAU1 condensate normalizes mTOR levels, ameliorates autophagy-lysosome function, and reduces aggregation of pathological proteins in cellular models of neurodegenerative diseases. These findings highlight the importance of balanced phase separation in physiological processes, suggesting that modulating STAU1 condensate may be a strategy to mitigate the progression of neurodegenerative diseases with STAU1 overabundance.

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.

Neuronal RNA processing: cross-talk between transcriptional regulation and RNA-binding proteins

In the nervous system, alternative RNA processing is particularly prevalent, which results in the expression of thousands of transcript variants found in no other tissue. Neuron-specific RNA-binding proteins co-transcriptionally regulate alternative splicing, alternative polyadenylation, and RNA editing, thereby shaping the RNA identity of nervous system cells. Recent evidence suggests that interactions between RNA-binding proteins and cis-regulatory elements such as promoters and enhancers play a role in the determination of neuron-specific expression profiles. Here, we discuss possible mechanisms through which transcription and RNA processing cross-talk to generate the uniquely complex neuronal transcriptome, with a focus on alternative 3'-end formation.

Aberrant protein aggregation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal disease. As its pathological mechanisms are not well understood, there are no efficient therapeutics for it at present. While it is highly heterogenous both etiologically and clinically, it has a common salient hallmark, i.e., aberrant protein aggregation (APA). The upstream pathogenesis and the downstream effects of APA in ALS are sophisticated and the investigation of this pathology would be of consequence for understanding ALS. In this paper, the pathomechanism of APA in ALS and the candidate treatment strategies for it are discussed.

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.

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.

Genetic Landscape of Amyotrophic Lateral Sclerosis in Czech Patients

Background

Genetic factors are involved in the pathogenesis of familial and sporadic amyotrophic lateral sclerosis (ALS) and constitute a link to its association with frontotemporal dementia (FTD). Gene-targeted therapies for some forms of ALS (C9orf72, SOD1) have recently gained momentum. Genetic architecture in Czech ALS patients has not been comprehensively assessed so far.

Objective

We aimed to deliver pilot data on the genetic landscape of ALS in our country.

Methods

A cohort of patients with ALS (n = 88), recruited from two Czech Neuromuscular Centers, was assessed for hexanucleotide repeat expansion (HRE) in C9orf72 and also for genetic variations in other 36 ALS-linked genes via next-generation sequencing (NGS). Nine patients (10.1%) had a familial ALS. Further, we analyzed two subgroups of sporadic patients - with concomitant FTD (n = 7) and with young-onset of the disease (n = 22).

Results

We detected the pathogenic HRE in C9orf72 in 12 patients (13.5%) and three other pathogenic variants in FUS, TARDBP and TBK1, each in one patient. Additional 7 novel and 9 rare known variants with uncertain causal significance have been detected in 15 patients. Three sporadic patients with FTD (42.9%) were harbouring a pathogenic variant (all HRE in C9orf72). Surprisingly, none of the young-onset sporadic patients harboured a pathogenic variant and we detected no pathogenic SOD1 variant in our cohort.

Conclusion

Our findings resemble those from other European populations, with the highest prevalence of HRE in the C9orf72 gene. Further, our findings suggest a possibility of a missing genetic variability among young-onset patients.

Regulation of DNA damage response by RNA/DNA-binding proteins: Implications for neurological disorders and aging

RNA-binding proteins (RBPs) are evolutionarily conserved across most forms of life, with an estimated 1500 RBPs in humans. Traditionally associated with post-transcriptional gene regulation, RBPs contribute to nearly every known aspect of RNA biology, including RNA splicing, transport, and decay. In recent years, an increasing subset of RBPs have been recognized for their DNA binding properties and involvement in DNA transactions. We refer to these RBPs with well-characterized DNA binding activity as RNA/DNA binding proteins (RDBPs), many of which are linked to neurological diseases. RDBPs are associated with both nuclear and mitochondrial DNA repair. Furthermore, the presence of intrinsically disordered domains in RDBPs appears to be critical for regulating their diverse interactions and plays a key role in controlling protein aggregation, which is implicated in neurodegeneration. In this review, we discuss the emerging roles of common RDBPs from the heterogeneous nuclear ribonucleoprotein (hnRNP) family, such as TAR DNA binding protein-43 (TDP43) and fused in sarcoma (FUS) in controlling DNA damage response (DDR). We also explore the implications of RDBP pathology in aging and neurodegenerative diseases and provide a prospective on the therapeutic potential of targeting RDBP pathology mediated DDR defects for motor neuron diseases and aging.

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.

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.

Mutation of the ALS-/FTD-Associated RNA-Binding Protein FUS Affects Axonal Development

Aberrant condensation and localization of the RNA-binding protein (RBP) fused in sarcoma (FUS) occur in variants of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Changes in RBP function are commonly associated with changes in axonal cytoskeletal organization and branching in neurodevelopmental disorders. Here, we asked whether branching defects also occur in vivo in a model of FUS-associated disease. We use two reported Xenopus models of ALS/FTD (of either sex), the ALS-associated mutant FUS(P525L) and a mimic of hypomethylated FUS, FUS(16R). Both mutants strongly reduced axonal complexity in vivo. We also observed an axon looping defect for FUS(P525L) in the target area, which presumably arises due to errors in stop cue signaling. To assess whether the loss of axon complexity also had a cue-independent component, we assessed axonal cytoskeletal integrity in vitro. Using a novel combination of fluorescence and atomic force microscopy, we found that mutant FUS reduced actin density in the growth cone, altering its mechanical properties. Therefore, FUS mutants may induce defects during early axonal development.

Liquid-liquid phase separation in diseases

Liquid-liquid phase separation (LLPS), an emerging biophysical phenomenon, can sequester molecules to implement physiological and pathological functions. LLPS implements the assembly of numerous membraneless chambers, including stress granules and P-bodies, containing RNA and protein. RNA-RNA and RNA-protein interactions play a critical role in LLPS. Scaffolding proteins, through multivalent interactions and external factors, support protein-RNA interaction networks to form condensates involved in a variety of diseases, particularly neurodegenerative diseases and cancer. Modulating LLPS phenomenon in multiple pathogenic proteins for the treatment of neurodegenerative diseases and cancer could present a promising direction, though recent advances in this area are limited. Here, we summarize in detail the complexity of LLPS in constructing signaling pathways and highlight the role of LLPS in neurodegenerative diseases and cancers. We also explore RNA modifications on LLPS to alter diseases progression because these modifications can influence LLPS of certain proteins or the formation of stress granules, and discuss the possibility of proper manipulation of LLPS process to restore cellular homeostasis or develop therapeutic drugs for the eradication of diseases. This review attempts to discuss potential therapeutic opportunities by elaborating on the connection between LLPS, RNA modification, and their roles in diseases.

Rare variant analyses validate known ALS genes in a multi-ethnic population and identifies ANTXR2 as a candidate in PLS

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting over 300,000 people worldwide. It is characterized by the progressive decline of the nervous system that leads to the weakening of muscles which impacts physical function. Approximately, 15% of individuals diagnosed with ALS have a known genetic variant that contributes to their disease. As therapies that slow or prevent symptoms continue to develop, such as antisense oligonucleotides, it is important to discover novel genes that could be targets for treatment. Additionally, as cohorts continue to grow, performing analyses in ALS subtypes, such as primary lateral sclerosis (PLS), becomes possible due to an increase in power. These analyses could highlight novel pathways in disease manifestation.

METHODS

Building on our previous discoveries using rare variant association analyses, we conducted rare variant burden testing on a substantially larger multi-ethnic cohort of 6,970 ALS patients, 166 PLS patients, and 22,524 controls. We used intolerant domain percentiles based on sub-region Residual Variation Intolerance Score (subRVIS) that have been described previously in conjunction with gene based collapsing approaches to conduct burden testing to identify genes that associate with ALS and PLS.

RESULTS

A gene based collapsing model showed significant associations with SOD1, TARDBP, and TBK1 (OR = 19.18, p = 3.67 × 10-39; OR = 4.73, p = 2 × 10-10; OR = 2.3, p = 7.49 × 10-9, respectively). These genes have been previously associated with ALS. Additionally, a significant novel control enriched gene, ALKBH3 (p = 4.88 × 10-7), was protective for ALS in this model. An intolerant domain-based collapsing model showed a significant improvement in identifying regions in TARDBP that associated with ALS (OR = 10.08, p = 3.62 × 10-16). Our PLS protein truncating variant collapsing analysis demonstrated significant case enrichment in ANTXR2 (p = 8.38 × 10-6).

CONCLUSIONS

In a large multi-ethnic cohort of 6,970 ALS patients, collapsing analyses validated known ALS genes and identified a novel potentially protective gene, ALKBH3. A first-ever analysis in 166 patients with PLS found a candidate association with loss-of-function mutations in ANTXR2.

High-content analysis of proteostasis capacity in cellular models of amyotrophic lateral sclerosis (ALS)

Disrupted proteome homeostasis (proteostasis) in amyotrophic lateral sclerosis (ALS) has been a major focus of research in the past two decades. However, the proteostasis processes that become disturbed in ALS are not fully understood. Obtaining more detailed knowledge of proteostasis disruption in association with different ALS-causing mutations will improve our understanding of ALS pathophysiology and may identify novel therapeutic targets and strategies for ALS patients. Here we describe the development and use of a novel high-content analysis (HCA) assay to investigate proteostasis disturbances caused by the expression of several ALS-causing gene variants. This assay involves the use of conformationally-destabilised mutants of firefly luciferase (Fluc) to examine protein folding/re-folding capacity in NSC-34 cells expressing ALS-associated mutations in the genes encoding superoxide dismutase-1 (SOD1A4V) and cyclin F (CCNFS621G). We demonstrate that these Fluc isoforms can be used in high-throughput format to report on reductions in the activity of the chaperone network that result from the expression of SOD1A4V, providing multiplexed information at single-cell resolution. In addition to SOD1A4V and CCNFS621G, NSC-34 models of ALS-associated TDP-43, FUS, UBQLN2, OPTN, VCP and VAPB mutants were generated that could be screened using this assay in future work. For ALS-associated mutant proteins that do cause reductions in protein quality control capacity, such as SOD1A4V, this assay has potential to be applied in drug screening studies to identify candidate compounds that can ameliorate this deficiency.

LncRNA NEAT1 promotes MPP+ induced injury of PC12 cells and accelerates the progression of Parkinson's disease in mice through FUS mediated inhibition of PI3K/AKT/mTOR signalling pathway

Long noncoding RNA nuclear-enriched abundant transcript 1 (NEAT1) is involved in the progression of Parkinson's disease (PD), but the specific regulatory role needs further exploration. This study showed that the expression of NEAT1 was upregulated in the cerebrospinal fluid (CSF) and peripheral blood of patients with different stages of PD. 1-Methyl-4-phenylpyridine (MPP)-treated PC 12 cells were transfected with si-NEAT1, and MPP treatment promoted cell apoptosis, oxidative stress and inflammatory factor secretion. Si-NEAT1 reversed the effects of MPP. NEAT1 silencing eliminated the effect of MPP on the protein expression levels of LC3-II and p62/SQSTM1. By using an online bioinformatics database, Fused in Sarcoma (FUS) was confirmed to be an RNA binding protein of NEAT1, and it was highly expressed in the CSF and peripheral blood of patients with PD. Si-FUS was transfected into MPP-treated PC 12 cells to detect cell apoptosis, oxidative stress, inflammatory factor secretion and autophagy, and the results were the same as those of transfection of si-NEAT1. Furthermore, MPP treatment reduced the phosphorylation levels of PI3K, Akt and mTOR, whereas si-FUS reversed the effects of MPP. In vivo, compared with the model group, the PD mice showed reduced NEAT1 and FUS expression levels and activated PI3K pathway after being injected with si-NEAT1. The brain tissue of NEAT1-silenced PD mice had decreased inflammatory infiltration and apoptosis and increased neurological scores. In conclusion, NEAT1 is involved in PD progression through FUS-mediated inhibition of the PI3K/AKT/mTOR signalling pathway.

Frontotemporal dementia-like disease progression elicited by seeded aggregation and spread of FUS

RNA binding proteins have emerged as central players in the mechanisms of many neurodegenerative diseases. In particular, a proteinopathy of fused in sarcoma (FUS) is present in some instances of familial Amyotrophic lateral sclerosis (ALS) and about 10% of sporadic Frontotemporal lobar degeneration (FTLD). Here we establish that focal injection of sonicated human FUS fibrils into brains of mice in which ALS-linked mutant or wild-type human FUS replaces endogenous mouse FUS is sufficient to induce focal cytoplasmic mislocalization and aggregation of mutant and wild-type FUS which with time spreads to distal regions of the brain. Human FUS fibril-induced FUS aggregation in the mouse brain of humanized FUS mice is accelerated by an ALS-causing FUS mutant relative to wild-type human FUS. Injection of sonicated human FUS fibrils does not induce FUS aggregation and subsequent spreading after injection into naïve mouse brains containing only mouse FUS, indicating a species barrier to human FUS aggregation and its prion-like spread. Fibril-induced human FUS aggregates recapitulate pathological features of FTLD including increased detergent insolubility of FUS and TAF15 and amyloid-like, cytoplasmic deposits of FUS that accumulate ubiquitin and p62, but not TDP-43. Finally, injection of sonicated FUS fibrils is shown to exacerbate age-dependent cognitive and behavioral deficits from mutant human FUS expression. Thus, focal seeded aggregation of FUS and further propagation through prion-like spread elicits FUS-proteinopathy and FTLD-like disease progression.

FUS reads histone H3K36me3 to regulate alternative polyadenylation

Complex organisms generate differential gene expression through the same set of DNA sequences in distinct cells. The communication between chromatin and RNA regulates cellular behavior in tissues. However, little is known about how chromatin, especially histone modifications, regulates RNA polyadenylation. In this study, we found that FUS was recruited to chromatin by H3K36me3 at gene bodies. The H3K36me3 recognition of FUS was mediated by the proline residues in the ZNF domain. After these proline residues were mutated or H3K36me3 was abolished, FUS dissociated from chromatin and bound more to RNA, resulting in an increase in polyadenylation sites far from stop codons genome-wide. A proline mutation corresponding to a mutation in amyotrophic lateral sclerosis contributed to the hyperactivation of mitochondria and hyperdifferentiation in mouse embryonic stem cells. These findings reveal that FUS is an H3K36me3 reader protein that links chromatin-mediated alternative polyadenylation to human disease.

Frontotemporal dementia-like disease progression elicited by seeded aggregation and spread of FUS

RNA binding proteins have emerged as central players in the mechanisms of many neurodegenerative diseases. In particular, a proteinopathy of fu sed in s arcoma (FUS) is present in some instances of familial Amyotrophic lateral sclerosis (ALS) and about 10% of sporadic FTLD. Here we establish that focal injection of sonicated human FUS fibrils into brains of mice in which ALS-linked mutant or wild-type human FUS replaces endogenous mouse FUS is sufficient to induce focal cytoplasmic mislocalization and aggregation of mutant and wild-type FUS which with time spreads to distal regions of the brain. Human FUS fibril-induced FUS aggregation in the mouse brain of humanized FUS mice is accelerated by an ALS-causing FUS mutant relative to wild-type human FUS. Injection of sonicated human FUS fibrils does not induce FUS aggregation and subsequent spreading after injection into naïve mouse brains containing only mouse FUS, indicating a species barrier to human FUS aggregation and its prion-like spread. Fibril-induced human FUS aggregates recapitulate pathological features of FTLD including increased detergent insolubility of FUS and TAF15 and amyloid-like, cytoplasmic deposits of FUS that accumulate ubiquitin and p62, but not TDP-43. Finally, injection of sonicated FUS fibrils is shown to exacerbate age-dependent cognitive and behavioral deficits from mutant human FUS expression. Thus, focal seeded aggregation of FUS and further propagation through prion-like spread elicits FUS-proteinopathy and FTLD-like disease progression.

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.

Mitigation of TDP-43 toxic phenotype by an RGNEF fragment in amyotrophic lateral sclerosis models

Aggregation of the RNA-binding protein TAR DNA binding protein (TDP-43) is a hallmark of TDP-proteinopathies including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). As TDP-43 aggregation and dysregulation are causative of neuronal death, there is a special interest in targeting this protein as a therapeutic approach. Previously, we found that TDP-43 extensively co-aggregated with the dual function protein GEF (guanine exchange factor) and RNA-binding protein rho guanine nucleotide exchange factor (RGNEF) in ALS patients. Here, we show that an N-terminal fragment of RGNEF (NF242) interacts directly with the RNA recognition motifs of TDP-43 competing with RNA and that the IPT/TIG domain of NF242 is essential for this interaction. Genetic expression of NF242 in a fruit fly ALS model overexpressing TDP-43 suppressed the neuropathological phenotype increasing lifespan, abolishing motor defects and preventing neurodegeneration. Intracerebroventricular injections of AAV9/NF242 in a severe TDP-43 murine model (rNLS8) improved lifespan and motor phenotype, and decreased neuroinflammation markers. Our results demonstrate an innovative way to target TDP-43 proteinopathies using a protein fragment with a strong affinity for TDP-43 aggregates and a mechanism that includes competition with RNA sequestration, suggesting a promising therapeutic strategy for TDP-43 proteinopathies such as ALS and FTD.

Evaluating emerging drugs in phase II & III for the treatment of amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic Lateral Sclerosis is a rapidly progressive motor neuron disorder causing severe disability and premature death. Owing to the advances in uncovering ALS pathophysiology, efficient clinical trial design and research advocacy program, several disease-modifying drugs have been approved for treating ALS. Despite this progress, ALS remains a rapidly disabling and life shortening condition. There is a critical need for more effective therapies.

AREAS COVERED

Here, we reviewed the emerging ALS therapeutics undergoing phase II & III clinical trials. To identify the investigational drugs, we searched ALS and phase II/III trials that are active and recruiting or not yet recruiting on clinicaltrials.gov and Pharmaprojects database.

EXPERT OPINION

The current pipeline is larger and more diverse than ever, with drugs targeting potential genetic and retroviral causes of ALS and drugs targeting a wide array of downstream pathways, including RNA metabolism, protein aggregation, integrated stress response and neuroinflammation.We remain most excited about those that target direct causes of ALS, e.g. antisense oligonucleotides targeting causative genes. Drugs that eliminate abnormal protein aggregates are also up-and-coming. Eventually, because of the heterogeneity of ALS pathophysiology, biomarkers that determine which biological events are most important for an individual ALS patient are needed.

Variability in SOD1-associated amyotrophic lateral sclerosis: geographic patterns, clinical heterogeneity, molecular alterations, and therapeutic implications

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of motor neurons, resulting in global health burden and limited post-diagnosis life expectancy. Although primarily sporadic, familial ALS (fALS) cases suggest a genetic basis. This review focuses on SOD1, the first gene found to be associated with fALS, which has been more recently confirmed by genome sequencing. While informative, databases such as ALSoD and STRENGTH exhibit regional biases. Through a systematic global examination of SOD1 mutations from 1993 to 2023, we found different geographic distributions and clinical presentations. Even though different SOD1 variants are expressed at different protein levels and have different half-lives and dismutase activities, these alterations lead to loss of function that is not consistently correlated with disease severity. Gain of function of toxic aggregates of SOD1 resulting from mutated SOD1 has emerged as one of the key contributors to ALS. Therapeutic interventions specifically targeting toxic gain of function of mutant SOD1, including RNA interference and antibodies, show promise, but a cure remains elusive. This review provides a comprehensive perspective on SOD1-associated ALS and describes molecular features and the complex genetic landscape of SOD1, highlighting its importance in determining diverse clinical manifestations observed in ALS patients and emphasizing the need for personalized therapeutic strategies.

Amyotrophic lateral sclerosis; clinical features, differential diagnosis and pathology

Amyotrophic lateral sclerosis (ALS) is a late-onset syndrome characterized by the progressive degeneration of both upper motor neurons (UMN) and lower motor neurons (LMN). ALS forms a clinical continuum with frontotemporal dementia (FTD), in which there are progressive language deficits or behavioral changes. The genetics and pathology underlying both ALS and FTD overlap as well, with cytoplasmatic misvocalization of TDP-43 as the hallmark. ALS is diagnosed by exclusion. Over the years several diagnostic criteria have been proposed, which in essence all require a history of slowly progressive motor symptoms, with UMN and LMN signs on neurological examination, clear spread of symptoms through the body, the exclusion of other disorder that cause similar symptoms and an EMG that it is compatible with LMN loss. ALS is heterogeneous disorder that may present in multitude ways, which makes the diagnosis challenging. Therefore, a systematic approach in the diagnostic process is required in line with the most common presentations. Subsequently, assessing whether there are cognitive and/or behavioral changes within the spectrum of FTD and lastly determining the cause is genetic. This chapter, an outline on how to navigate this 3 step process.

Updates on Disease Mechanisms and Therapeutics for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS), or Lou Gehrig's disease, is a motor neuron disease. In ALS, upper and lower motor neurons in the brain and spinal cord progressively degenerate during the course of the disease, leading to the loss of the voluntary movement of the arms and legs. Since its first description in 1869 by a French neurologist Jean-Martin Charcot, the scientific discoveries on ALS have increased our understanding of ALS genetics, pathology and mechanisms and provided novel therapeutic strategies. The goal of this review article is to provide a comprehensive summary of the recent findings on ALS mechanisms and related therapeutic strategies to the scientific audience. Several highlighted ALS research topics discussed in this article include the 2023 FDA approved drug for SOD1 ALS, the updated C9orf72 GGGGCC repeat-expansion-related mechanisms and therapeutic targets, TDP-43-mediated cryptic splicing and disease markers and diagnostic and therapeutic options offered by these recent discoveries.

RNP granules in ALS and neurodegeneration: From multifunctional membraneless organelles to therapeutic opportunities

Amyotrophic lateral sclerosis (ALS) and related neurodegenerative diseases are characterised by dysfunction of a host of RNA-binding proteins (RBPs) and a severely disrupted RNA metabolism. Recently, RBP-harbouring phase-separated complexes, ribonucleoprotein (RNP) granules, have come into the limelight as "crucibles" of neuronal pathology in ALS. RNP granules are indispensable for the multitude of regulatory processes underlying cellular RNA metabolism and serve as critical organisers of cellular biochemistry. Neurons, highly specialised cells, heavily rely on RNP granules for efficient trafficking, signalling and stress responses. Multiple RNP granule components, primarily RBPs such as TDP-43 and FUS, are affected by ALS mutations. However, even in the absence of mutations, RBP proteinopathies represent pathophysiological hallmarks of ALS. Given the high local concentrations of RBPs and RNAs, their weakened or enhanced interactions within RNP granules disrupt their homeostasis. Thus, the physiological process of phase separation and RNP granule formation, vital for maintaining the high-functioning state of neuronal cells, becomes their Achilles heel. Here, we will review the recent literature on the causes and consequences of abnormal RNP granule functioning in ALS and related disorders. In particular, we will summarise the evidence for the network-level dysfunction of RNP granules in these conditions and discuss considerations for therapeutic interventions to target RBPs, RNP granules and their network as a whole.

Evaluation of the Safety and Efficacy of Repeated Mesenchymal Stem Cell Transplantations in ALS Patients by Investigating Patients' Specific Immunological and Biochemical Biomarkers

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is an incurable disease. There are vigorous attempts to develop treatments to reduce the effects of this disease, and among these treatments is the transplantation of stem cells. This study aimed to retrospectively evaluate a mesenchymal stem cell (MSC) therapy cohort as a promising novel treatment modality by estimating some additional new parameters, such as immunological and biochemical factors.

METHODS

This study was designed as an open-label, one-arm cohort retrospective study to evaluate potential diagnostic biomarkers of repeated infusions of autologous-bone marrow-derived mesenchymal stem cells (BM-MSCs) in 15 confirmed patients with ALS, administered at a dose of 1 × 106 cells/kg BW with a one-month interval, in equal amounts in both an intravenous (IV) and intrathecal (IT) capacity simultaneously, via various biochemical (iron (Fe), ferritin, total-iron-binding capacity (TIBC), transferrin, and creatine kinase (CK)) and immunological parameters (tumor necrosis factor-alpha (TNF-α), neurofilament light chain (NFL), and glial-cell-derived neurotrophic factor (GDNF) levels, evaluated during the three-month follow-up period in serum and cerebrospinal fluid (CSF).

RESULTS

Our study indicated that, in the case of immunological biomarkers, TNF-α levels in the CSF showed a significant decrease at month three after transplantation compared with levels at month zero, and the p-value was p < 0.01. No statistically significant changes were observed for other immunological as well as biochemical parameters and a p-value of p > 0.05.

CONCLUSIONS

These results can indicate the potential benefit of stem cell transfusion in patients with ALS and suggest some diagnostic biomarkers. Several studies are required to approve these results.

U1 snRNP Biogenesis Defects in Neurodegenerative Diseases

The U1 small ribonucleoprotein (U1 snRNP) plays a pivotal role in the intricate process of gene expression, specifically within nuclear RNA processing. By initiating the splicing reaction and modulating 3'-end processing, U1 snRNP exerts precise control over RNA metabolism and gene expression. This ribonucleoparticle is abundantly present, and its complex biogenesis necessitates shuttling between the nuclear and cytoplasmic compartments. Over the past three decades, extensive research has illuminated the crucial connection between disrupted U snRNP biogenesis and several prominent human diseases, notably various neurodegenerative conditions. The perturbation of U1 snRNP homeostasis has been firmly established in diseases such as Spinal Muscular Atrophy, Pontocerebellar hypoplasia, and FUS-mediated Amyotrophic Lateral Sclerosis. Intriguingly, compelling evidence suggests a potential correlation in Fronto-temporal dementia and Alzheimer's disease as well. Although the U snRNP biogenesis pathway is conserved across all eukaryotic cells, neurons, in particular, appear to be highly susceptible to alterations in spliceosome homeostasis. In contrast, other cell types exhibit a greater resilience to such disturbances. This vulnerability underscores the intricate relationship between U1 snRNP dynamics and the health of neuronal cells, shedding light on potential avenues for understanding and addressing neurodegenerative disorders.

Physiological and pathological effects of phase separation in the central nervous system

Phase separation, also known as biomolecule condensate, participates in physiological processes such as transcriptional regulation, signal transduction, gene expression, and DNA damage repair by creating a membrane-free compartment. Phase separation is primarily caused by the interaction of multivalent non-covalent bonds between proteins and/or nucleic acids. The strength of molecular multivalent interaction can be modified by component concentration, the potential of hydrogen, posttranslational modification, and other factors. Notably, phase separation occurs frequently in the cytoplasm of mitochondria, the nucleus, and synapses. Phase separation in vivo is dynamic or stable in the normal physiological state, while abnormal phase separation will lead to the formation of biomolecule condensates, speeding up the disease progression. To provide candidate suggestions for the clinical treatment of nervous system diseases, this review, based on existing studies, carefully and systematically represents the physiological roles of phase separation in the central nervous system and its pathological mechanism in neurodegenerative diseases.

Pathological mechanisms of amyotrophic lateral Sclerosis

Amyotrophic lateral sclerosis refers to a neurodegenerative disease involving the motor system, the cause of which remains unexplained despite several years of research. Thus, the journey to understanding or treating amyotrophic lateral sclerosis is still a long one. According to current research, amyotrophic lateral sclerosis is likely not due to a single factor but rather to a combination of mechanisms mediated by complex interactions between molecular and genetic pathways. The progression of the disease involves multiple cellular processes and the interaction between different complex mechanisms makes it difficult to identify the causative factors of amyotrophic lateral sclerosis. Here, we review the most common amyotrophic lateral sclerosis-associated pathogenic genes and the pathways involved in amyotrophic lateral sclerosis, as well as summarize currently proposed potential mechanisms responsible for amyotrophic lateral sclerosis disease and their evidence for involvement in amyotrophic lateral sclerosis. In addition, we discuss current emerging strategies for the treatment of amyotrophic lateral sclerosis. Studying the emergence of these new therapies may help to further our understanding of the pathogenic mechanisms of the disease.

Molecular and cellular mechanisms of selective vulnerability in neurodegenerative diseases

The selective vulnerability of specific neuronal subtypes is a hallmark of neurodegenerative diseases. In this Review, I summarize our current understanding of the brain regions and cell types that are selectively vulnerable in different neurodegenerative diseases and describe the proposed underlying cell-autonomous and non-cell-autonomous mechanisms. I highlight how recent methodological innovations - including single-cell transcriptomics, CRISPR-based screens and human cell-based models of disease - are enabling new breakthroughs in our understanding of selective vulnerability. An understanding of the molecular mechanisms that determine selective vulnerability and resilience would shed light on the key processes that drive neurodegeneration and point to potential therapeutic strategies to protect vulnerable cell populations.

Molecular mechanisms and therapeutic strategies for neuromuscular diseases

Neuromuscular diseases encompass a heterogeneous array of disorders characterized by varying onset ages, clinical presentations, severity, and progression. While these conditions can stem from acquired or inherited causes, this review specifically focuses on disorders arising from genetic abnormalities, excluding metabolic conditions. The pathogenic defect may primarily affect the anterior horn cells, the axonal or myelin component of peripheral nerves, the neuromuscular junction, or skeletal and/or cardiac muscles. While inherited neuromuscular disorders have been historically deemed not treatable, the advent of gene-based and molecular therapies is reshaping the treatment landscape for this group of condition. With the caveat that many products still fail to translate the positive results obtained in pre-clinical models to humans, both the technological development (e.g., implementation of tissue-specific vectors) as well as advances on the knowledge of pathogenetic mechanisms form a collective foundation for potentially curative approaches to these debilitating conditions. This review delineates the current panorama of therapies targeting the most prevalent forms of inherited neuromuscular diseases, emphasizing approved treatments and those already undergoing human testing, offering insights into the state-of-the-art interventions.

Neurofilaments in Sporadic and Familial Amyotrophic Lateral Sclerosis: A Systematic Review and Meta-Analysis

BACKGROUND

Neurofilament proteins have been implicated to be altered in amyotrophic lateral sclerosis (ALS). The objectives of this study were to assess the diagnostic and prognostic utility of neurofilaments in ALS.

METHODS

Studies were conducted in electronic databases (PubMed/MEDLINE, Embase, Web of Science, and Cochrane CENTRAL) from inception to 17 August 2023, and investigated neurofilament light (NfL) or phosphorylated neurofilament heavy chain (pNfH) in ALS. The study design, enrolment criteria, neurofilament concentrations, test accuracy, relationship between neurofilaments in cerebrospinal fluid (CSF) and blood, and clinical outcome were recorded. The protocol was registered with PROSPERO, CRD42022376939.

RESULTS

Sixty studies with 8801 participants were included. Both NfL and pNfH measured in CSF showed high sensitivity and specificity in distinguishing ALS from disease mimics. Both NfL and pNfH measured in CSF correlated with their corresponding levels in blood (plasma or serum); however, there were stronger correlations between CSF NfL and blood NfL. NfL measured in blood exhibited high sensitivity and specificity in distinguishing ALS from controls. Both higher levels of NfL and pNfH either measured in blood or CSF were correlated with more severe symptoms as assessed by the ALS Functional Rating Scale Revised score and with a faster disease progression rate; however, only blood NfL levels were associated with shorter survival.

DISCUSSION

Both NfL and pNfH measured in CSF or blood show high diagnostic utility and association with ALS functional scores and disease progression, while CSF NfL correlates strongly with blood (either plasma or serum) and is also associated with survival, supporting its use in clinical diagnostics and prognosis. Future work must be conducted in a prospective manner with standardized bio-specimen collection methods and analytical platforms, further improvement in immunoassays for quantification of pNfH in blood, and the identification of cut-offs across the ALS spectrum and controls.

Discovery of SQSTM1/p62-dependent P-bodies that regulate the NLRP3 inflammasome

Autophagy and ribonucleoprotein granules, such as P-bodies (PBs) and stress granules, represent vital stress responses to maintain cellular homeostasis. SQSTM1/p62 phase-separated droplets are known to play critical roles in selective autophagy; however, it is unknown whether p62 can exist as another form in addition to its autophagic droplets. Here, we found that, under stress conditions, including proteotoxicity, endotoxicity, and oxidation, autophagic p62 droplets are transformed to a type of enlarged PBs, termed p62-dependent P-bodies (pd-PBs). p62 phase separation is essential for the nucleation of pd-PBs. Mechanistically, pd-PBs are triggered by enhanced p62 droplet formation upon stress stimulation through the interactions between p62 and DDX6, a DEAD-box ATPase. Functionally, pd-PBs recruit the NLRP3 inflammasome adaptor ASC to assemble the NLRP3 inflammasome and induce inflammation-associated cytotoxicity. Our study shows that p62 droplet-to-PB transformation acts as a stress response to activate the NLRP3 inflammasome process, suggesting that persistent pd-PBs lead to NLRP3-dependent inflammation toxicity.

Endogenous EWSR1 Exists in Two Visual Modalities That Reflect Its Associations with Nucleic Acids and Concentration at Sites of Active Transcription

EWSR1 is a member of the FET family of nucleic acid binding proteins that includes FUS and TAF15. Here, we report the systematic analysis of endogenous EWSR1's cellular organization in human cells. We demonstrate that EWSR1, which contains low complexity and nucleic acid binding domains, is present in cells in faster and slower-recovering fractions, indicative of a protein undergoing both rapid exchange and longer-term interactions. The employment of complementary high-resolution imaging approaches shows EWSR1 exists in two visual modalities, a distributed state which is present throughout the nucleoplasm, and a concentrated state consistent with the formation of foci. Both EWSR1 visual modalities localize with nascent RNA. EWSR1 foci concentrate in regions of euchromatin, adjacent to protein markers of transcriptional activation, and significantly colocalize with phosphorylated RNA polymerase II. Our results contribute to bridging the gap between our understanding of the biophysical and biochemical properties of FET proteins, including EWSR1, their functions as transcriptional regulators, and the participation of these proteins in tumorigenesis and neurodegenerative disease.

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.

Recent Research Trends in Neuroinflammatory and Neurodegenerative Disorders

Neuroinflammatory and neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), traumatic brain injury (TBI) and Amyotrophic lateral sclerosis (ALS) are chronic major health disorders. The exact mechanism of the neuroimmune dysfunctions of these disease pathogeneses is currently not clearly understood. These disorders show dysregulated neuroimmune and inflammatory responses, including activation of neurons, glial cells, and neurovascular unit damage associated with excessive release of proinflammatory cytokines, chemokines, neurotoxic mediators, and infiltration of peripheral immune cells into the brain, as well as entry of inflammatory mediators through damaged neurovascular endothelial cells, blood-brain barrier and tight junction proteins. Activation of glial cells and immune cells leads to the release of many inflammatory and neurotoxic molecules that cause neuroinflammation and neurodegeneration. Gulf War Illness (GWI) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are chronic disorders that are also associated with neuroimmune dysfunctions. Currently, there are no effective disease-modifying therapeutic options available for these diseases. Human induced pluripotent stem cell (iPSC)-derived neurons, astrocytes, microglia, endothelial cells and pericytes are currently used for many disease models for drug discovery. This review highlights certain recent trends in neuroinflammatory responses and iPSC-derived brain cell applications in neuroinflammatory disorders.

FUS unveiled in mitochondrial DNA repair and targeted ligase-1 expression rescues repair-defects in FUS-linked motor neuron disease

This study establishes the physiological role of Fused in Sarcoma (FUS) in mitochondrial DNA (mtDNA) repair and highlights its implications to the pathogenesis of FUS-associated neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). Endogenous FUS interacts with and recruits mtDNA Ligase IIIα (mtLig3) to DNA damage sites within mitochondria, a relationship essential for maintaining mtDNA repair and integrity in healthy cells. Using ALS patient-derived FUS mutant cell lines, a transgenic mouse model, and human autopsy samples, we discovered that compromised FUS functionality hinders mtLig3's repair role, resulting in increased mtDNA damage and mutations. These alterations cause various manifestations of mitochondrial dysfunction, particularly under stress conditions relevant to disease pathology. Importantly, rectifying FUS mutations in patient-derived induced pluripotent cells (iPSCs) preserves mtDNA integrity. Similarly, targeted introduction of human DNA Ligase 1 restores repair mechanisms and mitochondrial activity in FUS mutant cells, suggesting a potential therapeutic approach. Our findings unveil FUS's critical role in mitochondrial health and mtDNA repair, offering valuable insights into the mechanisms underlying mitochondrial dysfunction in FUS-associated motor neuron disease.

Invertebrate genetic models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a common adult-onset neurodegenerative disease characterized by the progressive death of motor neurons in the cerebral cortex, brain stem, and spinal cord. The exact mechanisms underlying the pathogenesis of ALS remain unclear. The current consensus regarding the pathogenesis of ALS suggests that the interaction between genetic susceptibility and harmful environmental factors is a promising cause of ALS onset. The investigation of putative harmful environmental factors has been the subject of several ongoing studies, but the use of transgenic animal models to study ALS has provided valuable information on the onset of ALS. Here, we review the current common invertebrate genetic models used to study the pathology, pathophysiology, and pathogenesis of ALS. The considerations of the usage, advantages, disadvantages, costs, and availability of each invertebrate model will also be discussed.

CRISPR/Cas9 system and its applications in nervous system diseases

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system is an acquired immune system of many bacteria and archaea, comprising CRISPR loci, Cas genes, and its associated proteins. This system can recognize exogenous DNA and utilize the Cas9 protein's nuclease activity to break DNA double-strand and to achieve base insertion or deletion by subsequent DNA repair. In recent years, multiple laboratory and clinical studies have revealed the therapeutic role of the CRISPR/Cas9 system in neurological diseases. This article reviews the CRISPR/Cas9-mediated gene editing technology and its potential for clinical application against neurological diseases.

RNA and the RNA-binding protein FUS act in concert to prevent TDP-43 spatial segregation

FUS and TDP-43 are two self-adhesive aggregation-prone mRNA-binding proteins whose pathological mutations have been linked to neurodegeneration. While TDP-43 and FUS form reversible mRNA-rich compartments in the nucleus, pathological mutations promote their respective cytoplasmic aggregation in neurons with no apparent link between the two proteins except their intertwined function in mRNA processing. By combining analyses in cellular context and at high resolution in vitro, we unraveled that TDP-43 is specifically recruited in FUS assemblies to form TDP-43-rich subcompartments but without reciprocity. The presence of mRNA provides an additional scaffold to promote the mixing between TDP-43 and FUS. Accordingly, we also found that the pathological truncated form of TDP-43, TDP-25, which has an impaired RNA-binding ability, no longer mixes with FUS. Together, these results suggest that the binding of FUS along nascent mRNAs enables TDP-43, which is highly aggregation-prone, to mix with FUS phase to form mRNA-rich subcompartments. A functional link between FUS and TDP-43 may explain their common implication in amyotrophic lateral sclerosis.

Increased expression of human antiviral protein MxA in FUS proteinopathy in amyotrophic lateral sclerosis

FUS mutations are one of the major mutations in familial amyotrophic lateral sclerosis (ALS). The pathological hallmark is FUS-positive neuronal cytoplasmic inclusions (FUS-NCI), known as FUS proteinopathy. Human myxovirus resistance protein 1 (MxA) is an IFN-induced dynamin-like GTPase that acts as antiviral factor. In this study, we examined the expression of MxA in neurons bearing FUS-NCI. We performed immunohistochemistry for FUS and MxA to examine the expression of MxA in two autopsy cases with different FUS gene mutations localized at the nuclear localization signal site (Case 1, H517P; Case 2, R521C). MxA. Most neurons bearing FUS-NCI have increased cytoplasmic MxA expression. Increased cytoplasmic MxA showed several distribution patterns in relation to FUS-NCIs such as the following: colocalization with NCI, distribution more widely than NCI, and different distribution peaks from NCI. Our results suggested that antiviral signaling IFNs are involved upstream in the formation of FUS-NCI in ALS-FUS patients.

Implications in Cancer of Nuclear Micro RNAs, Long Non-Coding RNAs, and Circular RNAs Bound by PRC2 and FUS

The eukaryotic genome is mainly transcribed into non-coding RNAs (ncRNAs), including different RNA biotypes, such as micro RNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), among others. Although miRNAs are assumed to act primarily in the cytosol, mature miRNAs have been reported and functionally characterized in the nuclei of different cells. Further, lncRNAs are important regulators of different biological processes in the cell nucleus as part of different ribonucleoprotein complexes. CircRNAs constitute a relatively less-characterized RNA biotype that has a circular structure as result of a back-splicing process. However, circRNAs have recently attracted attention in different scientific fields due to their involvement in various biological processes and pathologies. In this review, we will summarize recent studies that link to cancer miRNAs that have been functionally characterized in the cell nucleus, as well as lncRNAs and circRNAs that are bound by core components of the polycomb repressive complex 2 (PRC2) or the protein fused in sarcoma (FUS), highlighting mechanistic aspects and their diagnostic and therapeutic potential.

Zebrafish CCNF and FUS Mediate Stress-Specific Motor Responses

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by the degeneration of motor neurons. Mutations in the cyclin F (CCNF) and fused in sarcoma (FUS) genes have been associated with ALS pathology. In this study, we aimed to investigate the functional role of CCNF and FUS in ALS by using genome editing techniques to generate zebrafish models with genetic disruptions in these genes. Sequence comparisons showed significant homology between human and zebrafish CCNF and FUS proteins. We used CRISPR/Cas9 and TALEN-mediated genome editing to generate targeted disruptions in the zebrafish ccnf and fus genes. Ccnf-deficient zebrafish exhibited abnormal motor neuron development and axonal outgrowth, whereas Fus-deficient zebrafish did not exhibit developmental abnormalities or axonopathies in primary motor neurons. However, Fus-deficient zebrafish displayed motor impairments in response to oxidative and endoplasmic reticulum stress. The Ccnf-deficient zebrafish were only sensitized to endoplasmic reticulum stress, indicating that ALS genes have overlapping as well as unique cellular functions. These zebrafish models provide valuable platforms for studying the functional consequences of CCNF and FUS mutations in ALS pathogenesis. Furthermore, these zebrafish models expand the drug screening toolkit used to evaluate possible ALS treatments.

PP2A and GSK3 act as modifiers of FUS-ALS by modulating mitochondrial transport

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease which currently lacks effective treatments. Mutations in the RNA-binding protein FUS are a common cause of familial ALS, accounting for around 4% of the cases. Understanding the mechanisms by which mutant FUS becomes toxic to neurons can provide insight into the pathogenesis of both familial and sporadic ALS. We have previously observed that overexpression of wild-type or ALS-mutant FUS in Drosophila motor neurons is toxic, which allowed us to screen for novel genetic modifiers of the disease. Using a genome-wide screening approach, we identified Protein Phosphatase 2A (PP2A) and Glycogen Synthase Kinase 3 (GSK3) as novel modifiers of FUS-ALS. Loss of function or pharmacological inhibition of either protein rescued FUS-associated lethality in Drosophila. Consistent with a conserved role in disease pathogenesis, pharmacological inhibition of both proteins rescued disease-relevant phenotypes, including mitochondrial trafficking defects and neuromuscular junction failure, in patient iPSC-derived spinal motor neurons (iPSC-sMNs). In FUS-ALS flies, mice, and human iPSC-sMNs, we observed reduced GSK3 inhibitory phosphorylation, suggesting that FUS dysfunction results in GSK3 hyperactivity. Furthermore, we found that PP2A acts upstream of GSK3, affecting its inhibitory phosphorylation. GSK3 has previously been linked to kinesin-1 hyperphosphorylation. We observed this in both flies and iPSC-sMNs, and we rescued this hyperphosphorylation by inhibiting GSK3 or PP2A. Moreover, increasing the level of kinesin-1 expression in our Drosophila model strongly rescued toxicity, confirming the relevance of kinesin-1 hyperphosphorylation. Our data provide in vivo evidence that PP2A and GSK3 are disease modifiers, and reveal an unexplored mechanistic link between PP2A, GSK3, and kinesin-1, that may be central to the pathogenesis of FUS-ALS and sporadic forms of the disease.

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.

A mutation in the low-complexity domain of splicing factor hnRNPA1 linked to amyotrophic lateral sclerosis disrupts distinct neuronal RNA splicing networks

Amyotrophic lateral sclerosis (ALS) is a debilitating neurodegenerative disease characterized by loss of motor neurons. Human genetic studies have linked mutations in RNA-binding proteins as causative for this disease. The hnRNPA1 protein, a known pre-mRNA splicing factor, is mutated in some ALS patients. Here, two human cell models were generated to investigate how a mutation in the C-terminal low-complexity domain (LCD) of hnRNPA1 can cause splicing changes of thousands of transcripts that collectively are linked to the DNA damage response, cilium organization, and translation. We show that the hnRNPA1 D262V mutant protein binds to new binding sites on differentially spliced transcripts from genes that are linked to ALS. We demonstrate that this ALS-linked hnRNPA1 mutation alters normal RNA-dependent protein-protein interactions. Furthermore, cells expressing this hnRNPA1 mutant exhibit a cell aggregation phenotype, markedly reduced growth rates, changes in stress granule kinetics, and aberrant growth of neuronal processes. This study provides insight into how a single amino acid mutation in a splicing factor can alter RNA splicing networks of genes linked to ALS.

ASPSCR1-TFE3 reprograms transcription by organizing enhancer loops around hexameric VCP/p97

The t(X,17) chromosomal translocation, generating the ASPSCR1::TFE3 fusion oncoprotein, is the singular genetic driver of alveolar soft part sarcoma (ASPS) and some Xp11-rearranged renal cell carcinomas (RCCs), frustrating efforts to identify therapeutic targets for these rare cancers. Here, proteomic analysis identifies VCP/p97, an AAA+ ATPase with known segregase function, as strongly enriched in co-immunoprecipitated nuclear complexes with ASPSCR1::TFE3. We demonstrate that VCP is a likely obligate co-factor of ASPSCR1::TFE3, one of the only such fusion oncoprotein co-factors identified in cancer biology. Specifically, VCP co-distributes with ASPSCR1::TFE3 across chromatin in association with enhancers genome-wide. VCP presence, its hexameric assembly, and its enzymatic function orchestrate the oncogenic transcriptional signature of ASPSCR1::TFE3, by facilitating assembly of higher-order chromatin conformation structures demonstrated by HiChIP. Finally, ASPSCR1::TFE3 and VCP demonstrate co-dependence for cancer cell proliferation and tumorigenesis in vitro and in ASPS and RCC mouse models, underscoring VCP's potential as a novel therapeutic target.

[Optineurin and mitochondrial dysfunction in neurodegeneration]

Optineurin (OPTN) is a multifunctional protein playing a crucial role as a receptor in selective autophagy. OPTN gene mutations are linked to diseases such as normal-tension glaucoma and amyotrophic lateral sclerosis. Recognized as a critical receptor for mitophagy, OPTN is pivotal in selectively degrading damaged mitochondria. This process is essential to prevent their accumulation, the generation of reactive oxygen species, and the release of pro-apoptotic factors. Mitophagy's quality control is governed by the PINK1 kinase and the cytosolic ubiquitin ligase Parkin, whose mutations are associated with Parkinson's disease. This review highlights recent insights emphasizing OPTN's role in mitophagy and its potential involvement in neurodegenerative diseases.