FET proteins regulate lifespan and neuronal integrity

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Simple models to understand complex disease: 10 years of progress from Caenorhabditis elegans models of amyotrophic lateral sclerosis and frontotemporal lobar degeneration

The nematode Caenorhabditis elegans are a powerful model system to study human disease, with numerous experimental advantages including significant genetic and cellular homology to vertebrate animals, a short lifespan, and tractable behavioral, molecular biology and imaging assays. Beginning with the identification of SOD1 as a genetic cause of amyotrophic lateral sclerosis (ALS), C. elegans have contributed to a deeper understanding of the mechanistic underpinnings of this devastating neurodegenerative disease. More recently this work has expanded to encompass models of other types of ALS and the related disease frontotemporal lobar degeneration (FTLD-TDP), including those characterized by mutation or accumulation of the proteins TDP-43, C9orf72, FUS, HnRNPA2B1, ALS2, DCTN1, CHCHD10, ELP3, TUBA4A, CAV1, UBQLN2, ATXN3, TIA1, KIF5A, VAPB, GRN, and RAB38. In this review we summarize these models and the progress and insights from the last ten years of using C. elegans to study the neurodegenerative diseases ALS and FTLD-TDP.

Animal Models of FUS-Proteinopathy: A Systematic Review

Mutations that disrupt the function of the DNA/RNA-binding protein FUS could cause amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases. One of the key features in ALS pathogenesis is the formation of insoluble protein aggregates containing aberrant isoforms of the FUS protein in the cytoplasm of upper and lower motor neurons. Reproduction of human pathology in animal models is the main tool for studying FUS-associated pathology and searching for potential therapeutic agents for ALS treatment. In this review, we provide a systematic analysis of the role of FUS protein in ALS pathogenesis and an overview of the results of modelling FUS-proteinopathy in animals.

TDP-1 and FUST-1 co-inhibit exon inclusion and control fertility together with transcriptional regulation

Gene expression is a multistep process and crosstalk among regulatory layers plays an important role in coordinating gene expression. To identify functionally relevant gene expression coordination, we performed a systematic reverse-genetic interaction screen in C. elegans, combining RNA binding protein (RBP) and transcription factor (TF) mutants to generate over 100 RBP;TF double mutants. We identified many unexpected double mutant phenotypes, including two strong genetic interactions between the ALS-related RBPs, fust-1 and tdp-1, and the homeodomain TF ceh-14. Losing any one of these genes alone has no effect on the health of the organism. However, fust-1;ceh-14 and tdp-1;ceh-14 double mutants both exhibit strong temperature-sensitive fertility defects. Both double mutants exhibit defects in gonad morphology, sperm function, and oocyte function. RNA-Seq analysis of double mutants identifies ceh-14 as the main controller of transcript levels, while fust-1 and tdp-1 control splicing through a shared role in exon inhibition. A skipped exon in the polyglutamine-repeat protein pqn-41 is aberrantly included in tdp-1 mutants, and genetically forcing this exon to be skipped in tdp-1;ceh-14 double mutants rescues their fertility. Together our findings identify a novel shared physiological role for fust-1 and tdp-1 in promoting C. elegans fertility and a shared molecular role in exon inhibition.

TDP-1 and FUST-1 co-inhibit exon inclusion and control fertility together with transcriptional regulation

Gene expression is a multistep, carefully controlled process, and crosstalk between regulatory layers plays an important role in coordinating gene expression. To identify functionally relevant coordination between transcriptional and post-transcriptional gene regulation, we performed a systematic reverse-genetic interaction screen in C. elegans . We combined RNA binding protein (RBP) and transcription factor (TF) mutants, creating over 100 RBP; TF double mutants. This screen identified a variety of unexpected double mutant phenotypes, including two strong genetic interactions between the ALS-related RBPs, fust-1 and tdp-1 , and the homeodomain TF ceh-14 . Losing any one of these genes alone has no significant effect on the health of the organism. However, fust-1; ceh-14 and tdp-1; ceh-14 double mutants both exhibit strong temperature-sensitive fertility defects. Both double mutants exhibit defects in gonad morphology, sperm function, and oocyte function. RNA-seq analysis of double mutants identifies ceh-14 as the main controller of transcript levels, while fust-1 and tdp-1 control splicing through a shared role in exon inhibition. We identify a cassette exon in the polyglutamine-repeat protein pqn-41 which tdp-1 inhibits. Loss of tdp-1 causes the pqn-41 exon to be aberrantly included, and forced skipping of this exon in tdp-1; ceh-14 double mutants rescues fertility. Together our findings identify a novel shared physiological role for fust-1 and tdp-1 in promoting C. elegans fertility in a ceh-14 mutant background and reveal a shared molecular function of fust-1 and tdp-1 in exon inhibition.

Caenorhabditis elegans as a Model System to Study Human Neurodegenerative Disorders

In recent years, advances in science and technology have improved our quality of life, enabling us to tackle diseases and increase human life expectancy. However, longevity is accompanied by an accretion in the frequency of age-related neurodegenerative diseases, creating a growing burden, with pervasive social impact for human societies. The cost of managing such chronic disorders and the lack of effective treatments highlight the need to decipher their molecular and genetic underpinnings, in order to discover new therapeutic targets. In this effort, the nematode Caenorhabditis elegans serves as a powerful tool to recapitulate several disease-related phenotypes and provides a highly malleable genetic model that allows the implementation of multidisciplinary approaches, in addition to large-scale genetic and pharmacological screens. Its anatomical transparency allows the use of co-expressed fluorescent proteins to track the progress of neurodegeneration. Moreover, the functional conservation of neuronal processes, along with the high homology between nematode and human genomes, render C. elegans extremely suitable for the study of human neurodegenerative disorders. This review describes nematode models used to study neurodegeneration and underscores their contribution in the effort to dissect the molecular basis of human diseases and identify novel gene targets with therapeutic potential.

Invited review: Unearthing the mechanisms of age-related neurodegenerative disease using Caenorhabditis elegans

As human life expectancy increases, neurodegenerative diseases present a growing public health threat, for which there are currently few effective treatments. There is an urgent need to understand the molecular and genetic underpinnings of these disorders so new therapeutic targets can be identified. Here we present the argument that the simple nematode worm Caenorhabditis elegans is a powerful tool to rapidly study neurodegenerative disorders due to their short lifespan and vast array of genetic tools, which can be combined with characterization of conserved neuronal processes and behavior orthologous to those disrupted in human disease. We review how pre-existing C. elegans models provide insight into human neurological disease as well as an overview of current tools available to study neurodegenerative diseases in the worm, with an emphasis on genetics and behavior. We also discuss open questions that C. elegans may be particularly well suited for in future studies and how worms will be a valuable preclinical model to better understand these devastating neurological disorders.

Disrupted autophagy and neuronal dysfunction in C. elegans knockin models of FUS amyotrophic lateral sclerosis

How mutations in FUS lead to neuronal dysfunction in amyotrophic lateral sclerosis (ALS) patients remains unclear. To examine mechanisms underlying ALS FUS dysfunction, we generate C. elegans knockin models using CRISPR-Cas9-mediated genome editing, creating R524S and P525L ALS FUS models. Although FUS inclusions are not detected, ALS FUS animals show defective neuromuscular function and locomotion under stress. Unlike animals lacking the endogenous FUS ortholog, ALS FUS animals have impaired neuronal autophagy and increased SQST-1 accumulation in motor neurons. Loss of sqst-1, the C. elegans ortholog for ALS-linked, autophagy adaptor protein SQSTM1/p62, suppresses both neuromuscular and stress-induced locomotion defects in ALS FUS animals, but does not suppress neuronal autophagy defects. Therefore, autophagy dysfunction is upstream of, and not dependent on, SQSTM1 function in ALS FUS pathogenesis. Combined, our findings demonstrate that autophagy dysfunction likely contributes to protein homeostasis and neuromuscular defects in ALS FUS knockin animals.

An autoregulation loop in fust-1 for circular RNA regulation in Caenorhabditis elegans

Many circular RNAs (circRNAs) are differentially expressed in different tissues or cell types, suggestive of specific factors that regulate their biogenesis. Here, taking advantage of available mutation strains of RNA-binding proteins (RBPs) in Caenorhabditis elegans, I performed a screening of circRNA regulation in 13 conserved RBPs. Among them, loss of FUST-1, the homolog of Fused in Sarcoma (FUS), caused downregulation of multiple circRNAs. By rescue experiments, I confirmed FUST-1 as a circRNA regulator. Through RNA sequencing using circRNA-enriched samples, circRNAs targets regulated by FUST-1 were identified globally, with hundreds of them significantly altered. Furthermore, I showed that FUST-1 regulates circRNA formation with only small to little effect on the cognate linear mRNAs. When recognizing circRNA pre-mRNAs, FUST-1 can affect both exon-skipping and circRNA in the same genes. Moreover, I identified an autoregulation loop in fust-1, where FUST-1, isoform a (FUST-1A) promotes the skipping of exon 5 of its own pre-mRNA, which produces FUST-1, isoform b (FUST-1B) with different N-terminal sequences. FUST-1A is the functional isoform in circRNA regulation. Although FUST-1B has the same functional domains as FUST-1A, it cannot regulate either exon-skipping or circRNA formation. This study provided an in vivo investigation of circRNA regulation, which will be helpful to understand the mechanisms that govern circRNA formation.

Overexpression of an ALS-associated FUS mutation in C. elegans disrupts NMJ morphology and leads to defective neuromuscular transmission

The amyotrophic lateral sclerosis (ALS) neurodegenerative disorder has been associated with multiple genetic lesions, including mutations in the gene for fused in sarcoma (FUS), a nuclear-localized RNA/DNA-binding protein. Neuronal expression of the pathological form of FUS proteins in Caenorhabditis elegans results in mislocalization and aggregation of FUS in the cytoplasm, and leads to impairment of motility. However, the mechanisms by which the mutant FUS disrupts neuronal health and function remain unclear. Here we investigated the impact of ALS-associated FUS on motor neuron health using correlative light and electron microscopy, electron tomography, and electrophysiology. We show that ectopic expression of wild-type or ALS-associated human FUS impairs synaptic vesicle docking at neuromuscular junctions. ALS-associated FUS led to the emergence of a population of large, electron-dense, and filament-filled endosomes. Electrophysiological recording revealed reduced transmission from motor neurons to muscles. Together, these results suggest a pathological effect of ALS-causing FUS at synaptic structure and function organization.This article has an associated First Person interview with the first author of the paper.

Splicing Players Are Differently Expressed in Sporadic Amyotrophic Lateral Sclerosis Molecular Clusters and Brain Regions

Splicing is a tightly orchestrated process by which the brain produces protein diversity over time and space. While this process specializes and diversifies neurons, its deregulation may be responsible for their selective degeneration. In amyotrophic lateral sclerosis (ALS), splicing defects have been investigated at the singular gene level without considering the higher-order level, involving the entire splicing machinery. In this study, we analyzed the complete spectrum (396) of genes encoding splicing factors in the motor cortex (41) and spinal cord (40) samples from control and sporadic ALS (SALS) patients. A substantial number of genes (184) displayed significant expression changes in tissue types or disease states, were implicated in distinct splicing complexes and showed different topological hierarchical roles based on protein–protein interactions. The deregulation of one of these splicing factors has a central topological role, i.e., the transcription factor YBX1, which might also have an impact on stress granule formation, a pathological marker associated with ALS.

Neuro-Cells therapy improves motor outcomes and suppresses inflammation during experimental syndrome of amyotrophic lateral sclerosis in mice

Aims

Mutations in DNA/RNA‐binding factor (fused‐in‐sarcoma) FUS and superoxide dismutase‐1 (SOD‐1) cause amyotrophic lateral sclerosis (ALS). They were reproduced in SOD‐1‐G93A (SOD‐1) and new FUS[1‐359]‐transgenic (FUS‐tg) mice, where inflammation contributes to disease progression. The effects of standard disease therapy and anti‐inflammatory treatments were investigated using these mutants.

Methods

FUS‐tg mice or controls received either vehicle, or standard ALS treatment riluzole (8 mg/kg/day), or anti‐inflammatory drug a selective blocker of cyclooxygenase‐2 celecoxib (30 mg/kg/day) for six weeks, or a single intracerebroventricular (i.c.v.) infusion of Neuro‐Cells (a preparation of 1.39 × 10⁶ mesenchymal and hemopoietic human stem cells, containing 5 × 10⁵ of CD34⁺ cells), which showed anti‐inflammatory properties. SOD‐1 mice received i.c.v.‐administration of Neuro‐Cells or vehicle.

Results

All FUS‐tg‐treated animals displayed less marked reductions in weight gain, food/water intake, and motor deficits than FUS‐tg‐vehicle‐treated mice. Neuro‐Cell‐treated mutants had reduced muscle atrophy and lumbar motor neuron degeneration. This group but not celecoxib‐FUS‐tg‐treated mice had ameliorated motor performance and lumbar expression of microglial activation marker, ionized calcium‐binding adapter molecule‐1 (Iba‐1), and glycogen‐synthase‐kinase‐3ß (GSK‐3ß). The Neuro‐Cells‐treated‐SOD‐1 mice showed better motor functions than vehicle‐treated‐SOD‐1 group.

Conclusion

The neuropathology in FUS‐tg mice is sensitive to standard ALS treatments and Neuro‐Cells infusion. The latter improves motor outcomes in two ALS models possibly by suppressing microglial activation.

Transcriptome Analysis of Long Non-coding RNAs and Genes Encoding Paraspeckle Proteins During Human Ovarian Follicle Development

Emerging evidence indicated that many long non-coding (lnc)RNAs function in multiple biological processes and dysregulation of their expression can cause diseases. Most regulatory lncRNAs interact with biological macromolecules such as DNA, RNA, and protein. LncRNAs regulate gene expression through epigenetic modification, transcription, and posttranscription, through DNA methylation, histone modification, and chromatin remodeling. Interestingly, differential lncRNA expression profiles in human oocytes and cumulus cells was recently assessed, however, lncRNAs in human follicle development has not previously been described. In this study, transcriptome dynamics in human primordial, primary and small antral follicles were interrogated and revealed information of lncRNA genes. It is known that some lncRNAs form a complex with paraspeckle proteins and therefore, we extended our transcriptional analysis to include genes encoding paraspeckle proteins. Primordial, primary follicles and small antral follicles was isolated using laser capture micro-dissection from ovarian tissue donated by three women having ovarian tissue cryopreserved before chemotherapy. After RN sequencing, a bioinformatic class comparison was performed and primordial, primary and small antral follicles were found to express several lncRNA and genes encoding paraspeckle proteins. Of particular interest, we detected the lncRNAs XIST, NEAT1, NEAT2 (MALAT1), and GAS5. Moreover, we noted a high expression of FUS, TAF15, and EWS components of the paraspeckles, proteins that belong to the FET (previously TET) family of RNA-binding proteins and are implicated in central cellular processes such as regulation of gene expression, maintenance of genomic integrity, and mRNA/microRNA processing. We also interrogated the intra-ovarian localization of the FUS, TAF15, and EWS proteins using immunofluorescence. The presence and the dynamics of genes that encode lncRNA and paraspeckle proteins may suggest that these may mediate functions in the cyclic recruitment and differentiation of human follicles and could participate in biological processes known to be associated with lncRNAs and paraspeckle proteins, such as gene expression control, scaffold formation and epigenetic control through human follicle development. This comprehensive transcriptome analysis of lncRNAs and genes encoding paraspeckle proteins expressed in human follicles could potentially provide biomarkers of oocyte quality for the development of non-invasive tests to identify embryos with high developmental potential.