Mutant ribonucleic acid (RNA) molecules can be toxic to the cell, causing human disease through trans-acting dominant mechanisms. RNA toxicity was first described in myotonic dystrophy type 1, a ...multisystemic disorder caused by the abnormal expansion of a non-coding trinucleotide repeat sequence. The development of multiple and complementary animal models of disease has greatly contributed to clarifying the complex disease pathways mediated by toxic RNA molecules. RNA toxicity is not limited to myotonic dystrophy and spreads to an increasing number of human conditions, which share some unifying pathogenic events mediated by toxic RNA accumulation and disruption of RNA-binding proteins. The remarkable progress in the dissection of disease pathobiology resulted in the rational design of molecular therapies, which have been successfully tested in animal models. Toxic RNA diseases, and in particular myotonic dystrophy, clearly illustrate the critical contribution of animal models of disease in translational research: from gene mutation to disease mechanisms, and ultimately to therapy development. This article is part of a Special Issue entitled: Animal Models of Disease.
•Expanded RNA repeats can be deleterious, causing multi-systemic diseases.•Myotonic dystrophy is the prototype of an increasing number of toxic RNA disorders.•Animal models have elucidated the mechanisms of RNA toxicity.•Toxic RNAs usually accumulate in the nucleus and disrupt RNA-binding proteins.•The understanding of disease mechanisms allowed the design of rational therapies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Aims
Myotonic dystrophy type I (DM1) is one of the most frequent muscular dystrophies in adults. Although DM1 has long been considered mainly a muscle disorder, growing evidence suggests the ...involvement of peripheral nerves in the pathogenicity of DM1 raising the question of whether motoneurons (MNs) actively contribute to neuromuscular defects in DM1.
Methods
By using micropatterned 96‐well plates as a coculture platform, we generated a functional neuromuscular model combining DM1 and muscleblind protein (MBNL) knock‐out human‐induced pluripotent stem cells‐derived MNs and human healthy skeletal muscle cells.
Results
This approach led to the identification of presynaptic defects which affect the formation or stability of the neuromuscular junction at an early developmental stage. These neuropathological defects could be reproduced by the loss of RNA‐binding MBNL proteins, whose loss of function in vivo is associated with muscular defects associated with DM1. These experiments indicate that the functional defects associated with MNs can be directly attributed to MBNL family proteins. Comparative transcriptomic analyses also revealed specific neuronal‐related processes regulated by these proteins that are commonly misregulated in DM1.
Conclusions
Beyond the application to DM1, our approach to generating a robust and reliable human neuromuscular system should facilitate disease modelling studies and drug screening assays.
Myotonic dystrophy type 1 (DM1) is one of the most common hereditary muscular dystrophies in adult. In this study, we assessed the anterograde contribution of spinal motoneurons in the neuromuscular defects observed in DM1. By using micropatterned cocultures between human skeletal muscle cells and human‐induced pluripotent stem cells (hiPSC)‐spinal motoneurons derived from DM1 patients, our analysis revealed presynaptic defects including abnormal neuritogenesis, which affect the formation or stability of the neuromuscular junction. These defects can be reproduced by depleting muscleblind (MBNL) proteins whose loss‐of‐function is a key event in DM1 pathogenesis. Thus, our study highlighted the importance of considering the anterograde pathological contribution of spinal motoneurons in discovery future therapy for DM1.
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DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Herein, the effect of the insertion of a thin dielectric HfO2:Al2O3 (HAO) layer at different positions in the Pt/0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BCZT)/Au structure on the energy storage ...performance of the capacitors is investigated. A high storage performance is achieved through the insertion of a HAO layer between BCZT and Au layers. The insertion of the dielectric layer causes a depolarization field which results in a high linearity hysteresis loop with low energy dissipation. The Pt/BCZT/HAO/Au capacitors show an impressive energy storage density of 99.8 J cm−3 and efficiency of 71.0%, at an applied electric field of 750 kV cm−1. Further, no significant change in the energy storage properties is observed after passing 108 switching cycles through the capacitor. The presence of resistive switching (RS) in leakage current characteristics confirms the strong charge coupling between ferroelectric and insulator layers. The same trend of the RS ratio and the energy storage performance with the variation of the architecture of the devices suggests that the energy storage properties can be improved through the charge coupling between the layers. By combining ferroelectrics and dielectrics into one single structure, the proposed strategy provides an efficient way for developing highly efficient energy storage capacitors.
It is demonstrated that high‐performance energy storage devices can be achieved through integration of ferroelectric and dielectric thin films and can be further optimized through selection of proper architecture of the device. The Pt/BCZT/HAO/Au capacitors exhibit an energy storage density of 99.8 J cm−3 and efficiency of 71.0%, with no significant change in the energy storage properties observed after passing 108 switching cycles.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Trinucleotide expansions cause disease by both protein- and RNA-mediated mechanisms. Unexpectedly, we discovered that CAG expansion constructs express homopolymeric polyglutamine, polyalanine, and ...polyserine proteins in the absence of an ATG start codon. This repeat-associated non-ATG translation (RAN translation) occurs across long, hairpin-forming repeats in transfected cells or when expansion constructs are integrated into the genome in lentiviral-transduced cells and brains. Additionally, we show that RAN translation across human spinocerebellar ataxia type 8 (SCA8) and myotonic dystrophy type 1 (DM1) CAG expansion transcripts results in the accumulation of SCA8 polyalanine and DM1 polyglutamine expansion proteins in previously established SCA8 and DM1 mouse models and human tissue. These results have implications for understanding fundamental mechanisms of gene expression. Moreover, these toxic, unexpected, homopolymeric proteins now should be considered in pathogenic models of microsatellite disorders.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The RNA-mediated disease model for myotonic dystrophy (DM) proposes that microsatellite C(C)TG expansions express toxic RNAs that disrupt splicing regulation by altering MBNL1 and CELF1 activities. ...While this model explains DM manifestations in muscle, less is known about the effects of C(C)UG expression on the brain. Here, we report that Mbnl2 knockout mice develop several DM-associated central nervous system (CNS) features including abnormal REM sleep propensity and deficits in spatial memory. Mbnl2 is prominently expressed in the hippocampus and Mbnl2 knockouts show a decrease in NMDA receptor (NMDAR) synaptic transmission and impaired hippocampal synaptic plasticity. While Mbnl2 loss did not significantly alter target transcript levels in the hippocampus, misregulated splicing of hundreds of exons was detected using splicing microarrays, RNA-seq, and HITS-CLIP. Importantly, the majority of the Mbnl2-regulated exons examined were similarly misregulated in DM. We propose that major pathological features of the DM brain result from disruption of the MBNL2-mediated developmental splicing program.
► Muscleblind-like 2 regulates alternative splicing in the brain ► Developmental regulation of splicing is disrupted in Mbnl2 knockout mice ► RNAs targeted by MBNL2 are misspliced in the myotonic dystrophy brain
Myotonic dystrophy, a disease caused by toxic RNAs, profoundly affects brain function. In this Article, Charizanis et al. demonstrate that the effect on brain function results from loss of muscleblind-like 2 RNA splicing regulation during brain development.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Myotonic dystrophy type 1 (DM1) is a severe neuromuscular disease mediated by a toxic gain of function of mutant RNAs. The neuropsychological manifestations affect multiple domains of cognition and ...behavior, but their etiology remains elusive. Transgenic DMSXL mice carry the DM1 mutation, show behavioral abnormalities, and express low levels of GLT1, a critical regulator of glutamate concentration in the synaptic cleft. However, the impact of glutamate homeostasis on neurotransmission in DM1 remains unknown. We confirmed reduced glutamate uptake in the DMSXL hippocampus. Patch clamp recordings in hippocampal slices revealed increased amplitude of tonic glutamate currents in DMSXL CA1 pyramidal neurons and DG granule cells, likely mediated by higher levels of ambient glutamate. Unexpectedly, extracellular GABA levels and tonic current were also elevated in DMSXL mice. Finally, we found evidence of synaptic dysfunction in DMSXL mice, suggestive of abnormal short-term plasticity, illustrated by an altered LTP time course in DG and in CA1. Synaptic dysfunction was accompanied by RNA foci accumulation in localized areas of the hippocampus and by the mis-splicing of candidate genes with relevant functions in neurotransmission. Molecular and functional changes triggered by toxic RNA may induce synaptic abnormalities in restricted brain areas that favor neuronal dysfunction.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Expanded, non-coding RNAs can exhibit a deleterious gain-of-function causing human disease through abnormal interactions with RNA-binding proteins. Myotonic dystrophy (DM), the prototypical example ...of an RNA-dominant disorder, is mediated by trinucleotide repeat-containing transcripts that deregulate alternative splicing. Spliceopathy has therefore been a major focus of DM research. However, changes in gene expression, protein translation and micro-RNA metabolism may also contribute to disease pathology. The exciting finding of bidirectional transcription and non-conventional RNA translation of trinucleotide repeat sequences points to a new scenario, in which DM is not mediated by one single expanded RNA transcript, but involves multiple pathogenic elements and pathways. The study of the growing number of human diseases associated with toxic repeat-containing transcripts provides important insight into the understanding of the complex pathways of RNA toxicity. This review describes some of the recent advances in the understanding of the molecular mechanisms behind DM and other RNA-dominant disorders.
Intensive effort has been directed toward the modeling of myotonic dystrophy (DM) in mice, in order to reproduce human disease and to provide useful tools to investigate molecular and cellular ...pathogenesis and test efficient therapies. Mouse models have contributed to dissect the multifaceted impact of the DM mutation in various tissues, cell types and in a pleiotropy of pathways, through the expression of toxic RNA transcripts. Changes in alternative splicing, transcription, translation, intracellular RNA localization, polyadenylation, miRNA metabolism and phosphorylation of disease intermediates have been described in different tissues. Some of these events have been directly associated with specific disease symptoms in the skeletal muscle and heart of mice, offering the molecular explanation for individual disease phenotypes. In the central nervous system (CNS), however, the situation is more complex. We still do not know how the molecular abnormalities described translate into CNS dysfunction, nor do we know if the correction of individual molecular events will provide significant therapeutic benefits. The variability in model design and phenotypes described so far requires a thorough and critical analysis. In this review we discuss the recent contributions of mouse models to the understanding of neuromuscular aspects of disease, therapy development, and we provide a reflective assessment of our current limitations and pressing questions that remain unanswered.
DNA repeat expansions can result in the production of toxic RNA. RNA toxicity has been best characterised in the context of myotonic dystrophy. Nearly 20 mouse models have contributed significant and ...complementary insights into specific aspects of this novel disease mechanism. These models provide a unique resource to test pharmacological, anti-sense, and gene-therapy therapeutic strategies that target specific events of the pathobiological cascade. Further proof-of-principle concept studies and preclinical experiments require critical and thorough analysis of the multiple myotonic dystrophy transgenic lines available. This review provides in-depth assessment of the molecular and phenotypic features of these models and their contribution towards the dissection of disease mechanisms, and compares them with the human condition. More importantly, it provides critical assessment of their suitability and limitations for preclinical testing of emerging therapeutic strategies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
Brain dysfunction in myotonic dystrophy type 1 (DM1), the prototype of toxic RNA disorders, has been mainly attributed to neuronal RNA misprocessing, while little attention has been given to ...non-neuronal brain cells. Here, using a transgenic mouse model of DM1 that expresses mutant RNA in various brain cell types (neurons, astroglia, and oligodendroglia), we demonstrate that astrocytes exhibit impaired ramification and polarization in vivo and defects in adhesion, spreading, and migration. RNA-dependent toxicity and phenotypes are also found in human transfected glial cells. In line with the cell phenotypes, molecular analyses reveal extensive expression and accumulation of toxic RNA in astrocytes, which result in RNA spliceopathy that is more severe than in neurons. Astrocyte missplicing affects primarily transcripts that regulate cell adhesion, cytoskeleton, and morphogenesis, and it is confirmed in human brain tissue. Our findings demonstrate that DM1 impacts astrocyte cell biology, possibly compromising their support and regulation of synaptic function.
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