Vulnerability of microRNA biogenesis in FTD-ALS

Role of Retroelements in Frontotemporal Dementia Development

Frontotemporal dementia (FTD) develops in proteinopathies involving TDP-43 (transactive response DNA-binding protein 43 kDa), tau, and FUS (fused in sarcoma) proteins, which possess antiviral properties and exert inhibitory effects on human transposable elements. Viruses and aging have been suggested to trigger FTD by activating specific retroelements. FTD is associated with multiple single nucleotide polymorphisms (SNPs), most located in intergenic and regulatory regions where many transposable element genes are found. Therefore, genetic predisposition to FTD may influence the interaction between retroelements and the TDP-43, tau, and FUS proteins, causing pathological conformation changes and aggregate formation. Subsequently, these aggregates lose their ability to inhibit retroelements, leading to the activation of transposable elements. This creates a harmful negative feedback loop in which TDP-43, tau, and FUS protein expressions are further enhanced by retroelement transcripts and proteins, resulting in protein aggregate accumulation and pathological disease progression. Hence, epigenetic inhibition of pathologically activated retroelements using micro-ribonucleic acids (microRNAs) derived from transposable elements has been proposed as a potential treatment for FTD. Finally, a review of the current scientific literature identified 13 appropriate microRNAs (miR-1246, -181c, -330, -345-5p, -361, -548a-3p, -548b-5p, -548c-5p, -571, -588, -659-3p, -708-3p, -887).

Drosha-dependent microRNAs modulate FUS-mediated neurodegeneration in vivo

Mutations in the Fused in Sarcoma (FUS) gene cause the familial and progressive form of amyotrophic lateral sclerosis (ALS). FUS is a nuclear RNA-binding protein involved in RNA processing and the biogenesis of a specific set of microRNAs. Here we report that Drosha and two previously uncharacterized Drosha-dependent miRNAs are strong modulators of FUS expression and prevent the cytoplasmic segregation of insoluble mutant FUS in vivo. We demonstrate that depletion of Drosha mitigates FUS-mediated degeneration, survival and motor defects in Drosophila. Mutant FUS strongly interacts with Drosha and causes its cytoplasmic mis-localization into the insoluble FUS inclusions. Reduction in Drosha levels increases the solubility of mutant FUS. Interestingly, we found two Drosha dependent microRNAs, miR-378i and miR-6832-5p, which differentially regulate the expression, solubility and cytoplasmic aggregation of mutant FUS in iPSC neurons and mammalian cells. More importantly, we report different modes of action of these miRNAs against mutant FUS. Whereas miR-378i may regulate mutant FUS inclusions by preventing G3BP-mediated stress granule formation, miR-6832-5p may affect FUS expression via other proteins or pathways. Overall, our research reveals a possible association between ALS-linked FUS mutations and the Drosha-dependent miRNA regulatory circuit, as well as a useful perspective on potential ALS treatment via microRNAs.

Systematic review and meta-analysis on microRNAs in amyotrophic lateral sclerosis

MicroRNAs (miRNAs) exhibit a crucial role in the pathogenesis and progress of neurodegenerative disorders. Recent studies have shown abnormal levels of miRNA expression in patients with amyotrophic lateral sclerosis (ALS). Clinical data also confirmed that miRNAs in these patients are inconsistent across studies. A comprehensive systematic review and meta-analysis of current studies can help recognize the important roles of miRNAs during ALS development. Therefore, we initially aimed to perform a systematic literature review on the muscle or serum miRNAs in patients with ALS and healthy individuals. Subsequently, we quantitatively summarized the clinical data of muscle or serum miRNA of patients with ALS and healthy individuals using a meta-analytical technique. 11 studies comprising 281 patients with ALS and 244 healthy control (HC) controls were identified from PubMed and Web of Science for meta-analysis. A systematic review revealed that miRNA levels are closely associated with the occurrence of ALS disease. The expression levels of the most relevant miRNAs were either increased or decreased. The random-effects meta-analysis indicated that the levels of miR-206, miR-133b, and miR-338-3p were significantly elevated in patients with ALS than in HC subjects. By contrast, there was no significant differences in the miR-133a levels between patients with ALS and HC subjects. Collectively, our outcomes demonstrated that serum miR-206, miR-133b, and miR-338-3p were significantly increased in patients with ALS. We speculated that the increased expression levels of miR-206, miR-133b and miR-338-3p are potential promising biomarkers for ALS.

TDP-43 Proteinopathy Specific Biomarker Development

TDP-43 is the primary or secondary pathological hallmark of neurodegenerative diseases, such as amyotrophic lateral sclerosis, half of frontotemporal dementia cases, and limbic age-related TDP-43 encephalopathy, which clinically resembles Alzheimer's dementia. In such diseases, a biomarker that can detect TDP-43 proteinopathy in life would help to stratify patients according to their definite diagnosis of pathology, rather than in clinical subgroups of uncertain pathology. For therapies developed to target pathological proteins that cause the disease a biomarker to detect and track the underlying pathology would greatly enhance such undertakings. This article reviews the latest developments and outlooks of deriving TDP-43-specific biomarkers from the pathophysiological processes involved in the development of TDP-43 proteinopathy and studies using biosamples from clinical entities associated with TDP-43 pathology to investigate biomarker candidates.

MicroRNA expression within neuronal-derived small extracellular vesicles in frontotemporal degeneration

MicroRNAs (miRNAs) are small non-coding RNA that are powerful regulators of gene expression and can affect the expression of hundreds of genes. miRNAs can be packed in small extracellular vesicles (SEV) and released into the extracellular space by neurons and microglia to act locally as well as pass through the blood-brain barrier and act systemically. We sought to understand the differences in neuronal SEV miRNA expression between frontotemporal dementia (FTD), Alzheimer's disease (AD), and healthy aging. Plasma was obtained from FTD, AD, and healthy aging participants that were matched based on age, sex, and race/ethnicity. Additionally, a subset of participants also provided paired cerebrospinal fluid samples to compare neuronal SEV miRNAs in plasma and cerebrospinal fluid. Neuronal SEV were isolated using differential ultracentrifugation and antibody conjugated Dynabeads® for the neuronal surface marker, L1CAM. RNA sequencing was performed. 12 FTD, 11 with AD, and 10 healthy aging participants were enrolled in the study. In FTD, SEV miRNA-181c was downregulated compared to healthy controls. In AD, miRNA-122 and miRNA-3591 were downregulated compared to those in healthy controls and FTD. Using an FDR <0.2, only miRNA-21-5p was found to have increased expression in the cerebrospinal fluid compared to plasma in a group of AD and FTD participants. SEV miRNA-181c is significantly downregulated in FTD compared to healthy controls and may mediate its effects through microglial-directed neuroinflammation and interaction with TAR DNA-binding protein 43 (TDP-43) based on pathway analysis. Additionally, the FOXO and Hippo pathways may be important mediators of FTD, based on pathway analysis. Lastly, because only one SEV miRNA was differentially expressed between the plasma and cerebrospinal fluid in paired samples, plasma represents an appropriate biofluid for studying neuronal SEV miRNA.

Whole-genome sequencing reveals that variants in the Interleukin 18 Receptor Accessory Protein 3'UTR protect against ALS

The noncoding genome is substantially larger than the protein-coding genome but has been largely unexplored by genetic association studies. Here, we performed region-based rare variant association analysis of >25,000 variants in untranslated regions of 6,139 amyotrophic lateral sclerosis (ALS) whole genomes and the whole genomes of 70,403 non-ALS controls. We identified interleukin-18 receptor accessory protein (IL18RAP) 3' untranslated region (3'UTR) variants as significantly enriched in non-ALS genomes and associated with a fivefold reduced risk of developing ALS, and this was replicated in an independent cohort. These variants in the IL18RAP 3'UTR reduce mRNA stability and the binding of double-stranded RNA (dsRNA)-binding proteins. Finally, the variants of the IL18RAP 3'UTR confer a survival advantage for motor neurons because they dampen neurotoxicity of human induced pluripotent stem cell (iPSC)-derived microglia bearing an ALS-associated expansion in C9orf72, and this depends on NF-κB signaling. This study reveals genetic variants that protect against ALS by reducing neuroinflammation and emphasizes the importance of noncoding genetic association studies.

MicroRNA expression in animal models of amyotrophic lateral sclerosis and potential therapeutic approaches

A review of recent animal models of amyotrophic lateral sclerosis showed a large number of miRNAs had altered levels of expression in the brain and spinal cord, motor neurons of spinal cord and brainstem, and hypoglossal, facial, and red motor nuclei and were mostly upregulated. Among the miRNAs found to be upregulated in two of the studies were miR-21, miR-155, miR-125b, miR-146a, miR-124, miR-9, and miR-19b, while those downregulated in two of the studies included miR-146a, miR-29, miR-9, and miR-125b. A change of direction in miRNA expression occurred in some tissues when compared (e.g., miR-29b-3p in cerebellum and spinal cord of wobbler mice at 40 days), or at different disease stages (e.g., miR-200a in spinal cord of SOD1(G93A) mice at 95 days vs. 108 and 112 days). In the animal models, suppression of miR-129-5p resulted in increased lifespan, improved muscle strength, reduced neuromuscular junction degeneration, and tended to improve motor neuron survival in the SOD1(G93A) mouse model. Suppression of miR-155 was also associated with increased lifespan, while lowering of miR-29a tended to improve lifespan in males and increase muscle strength in SOD1(G93A) mice. Overexpression of members of miR-17~92 cluster improved motor neuron survival in SOD1(G93A) mice. Treatment with an artificial miRNA designed to target hSOD1 increased lifespan and improved muscle strength in SOD1(G93A) animals. Further studies with animal models of amyotrophic lateral sclerosis are warranted to validate these findings and identify specific miRNAs whose suppression or directed against hSOD1 results in increased lifespan, improved muscle strength, reduced neuromuscular junction degeneration, and improved motor neuron survival in SOD1(G93A) animals.

Circulating miR-181 is a prognostic biomarker for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a relentless neurodegenerative disease of the human motor neuron system, where variability in progression rate limits clinical trial efficacy. Therefore, better prognostication will facilitate therapeutic progress. In this study, we investigated the potential of plasma cell-free microRNAs (miRNAs) as ALS prognostication biomarkers in 252 patients with detailed clinical phenotyping. First, we identified, in a longitudinal cohort, miRNAs whose plasma levels remain stable over the course of disease. Next, we showed that high levels of miR-181, a miRNA enriched in neurons, predicts a greater than two-fold risk of death in independent discovery and replication cohorts (126 and 122 patients, respectively). miR-181 performance is similar to neurofilament light chain (NfL), and when combined together, miR-181 + NfL establish a novel RNA-protein biomarker pair with superior prognostication capacity. Therefore, plasma miR-181 alone and a novel miRNA-protein biomarker approach, based on miR-181 + NfL, boost precision of patient stratification. miR-181-based ALS biomarkers encourage additional validation and might enhance the power of clinical trials.

RNA Deregulation in Amyotrophic Lateral Sclerosis: The Noncoding Perspective

RNA metabolism is central to cellular physiopathology. Almost all the molecular pathways underpinning biological processes are affected by the events governing the RNA life cycle, ranging from transcription to degradation. The deregulation of these processes contributes to the onset and progression of human diseases. In recent decades, considerable efforts have been devoted to the characterization of noncoding RNAs (ncRNAs) and to the study of their role in the homeostasis of the nervous system (NS), where they are highly enriched. Acting as major regulators of gene expression, ncRNAs orchestrate all the steps of the differentiation programs, participate in the mechanisms underlying neural functions, and are crucially implicated in the development of neuronal pathologies, among which are neurodegenerative diseases. This review aims to explore the link between ncRNA dysregulation and amyotrophic lateral sclerosis (ALS), the most frequent motoneuron (MN) disorder in adults. Notably, defective RNA metabolism is known to be largely associated with this pathology, which is often regarded as an RNA disease. We also discuss the potential role that these transcripts may play as diagnostic biomarkers and therapeutic targets.

Circulating microRNAs as potential biomarkers and therapeutic targets in spinal muscular atrophy

Spinal muscular atrophy (SMA), a leading genetic cause of infant death, is a neurodegenerative disease characterized by the selective loss of particular groups of motor neurons (MNs) in the anterior horn of the spinal cord with progressive muscle wasting. SMA is caused by a deficiency of the survival motor neuron (SMN) protein due to a homozygous deletion or mutation of the SMN1 gene. However, the molecular mechanisms whereby the SMN complex regulates MN functions are not fully elucidated. Emerging studies on SMA pathogenesis have turned the attention of researchers to RNA metabolism, given that increasingly identified SMN-associated modifiers are involved in both coding and non-coding RNA (ncRNA) processing. Among various ncRNAs, microRNAs (miRNAs) are the most studied in terms of regulation of posttranscriptional gene expression. Recently, the discovery that miRNAs are critical to MN function and survival led to the study of dysregulated miRNAs in SMA pathogenesis. Circulating miRNAs have drawn attention as a readily available biomarker due to their property of being clinically detectable in numerous human biofluids through non-invasive approaches. As there are recent promising findings from novel miRNA-based medicines, this article presents an extensive review of the most up-to-date studies connecting specific miRNAs to SMA pathogenesis and the potential applications of miRNAs as biomarkers and therapeutic targets for SMA.

Gene of the month: DICER1: ruler and controller

DICER1 is a highly conserved RNaseIII endoribonuclease that has a critical role in the biogenesis of microRNAs (miRNAs). miRNAs are small regulatory RNAs responsible for post-transcriptional gene silencing, controlling more than half of human protein-coding genes. This is achieved through the targeting and regulation of complementary RNA transcripts and has a well-documented role in post-transcriptional gene regulation and transposon repression. DICER1 deficiency results in dysregulation of miRNAs, changing the expression of many genes. DICER1 syndrome represents a collection of benign and malignant tumours arising from an autosomally inherited germline mutation leading to an inherited predisposition to cancer. The syndrome represents an unusual form of Knudson's two-hit hypothesis, where individuals with a pathogenic germline DICER1 variant acquire a second trans-somatic missense DICER1 mutation. This somatic mutation appears to have to occur in one of five hotspots codons and may contribute towards the incomplete penetrance observed within DICER1 syndrome families. In this case, DICER1 is haploinsuffcient with only one deletion required and partial loss of function being advantageous to tumours over complete loss of function. As increasing data emerge reaffirming the pivotal role of DICER1 in the maintenance of human physiology, DICER1 is likely to become an increasingly attractive target for novel therapeutic strategies.

Human genetics and neuropathology suggest a link between miR-218 and amyotrophic lateral sclerosis pathophysiology

Motor neuron-specific microRNA-218 (miR-218) has recently received attention because of its roles in mouse development. However, miR-218 relevance to human motor neuron disease was not yet explored. Here, we demonstrate by neuropathology that miR-218 is abundant in healthy human motor neurons. However, in amyotrophic lateral sclerosis (ALS) motor neurons, miR-218 is down-regulated and its mRNA targets are reciprocally up-regulated (derepressed). We further identify the potassium channel Kv10.1 as a new miR-218 direct target that controls neuronal activity. In addition, we screened thousands of ALS genomes and identified six rare variants in the human miR-218-2 sequence. miR-218 gene variants fail to regulate neuron activity, suggesting the importance of this small endogenous RNA for neuronal robustness. The underlying mechanisms involve inhibition of miR-218 biogenesis and reduced processing by DICER. Therefore, miR-218 activity in motor neurons may be susceptible to failure in human ALS, suggesting that miR-218 may be a potential therapeutic target in motor neuron disease.

Connecting RNA-Modifying Similarities of TDP-43, FUS, and SOD1 with MicroRNA Dysregulation Amidst A Renewed Network Perspective of Amyotrophic Lateral Sclerosis Proteinopathy

Beyond traditional approaches in understanding amyotrophic lateral sclerosis (ALS), multiple recent studies in RNA-binding proteins (RBPs)-including transactive response DNA-binding protein (TDP-43) and fused in sarcoma (FUS)-have instigated an interest in their function and prion-like properties. Given their prominence as hallmarks of a highly heterogeneous disease, this prompts a re-examination of the specific functional interrelationships between these proteins, especially as pathological SOD1-a non-RBP commonly associated with familial ALS (fALS)-exhibits similar properties to these RBPs including potential RNA-regulatory capabilities. Moreover, the cytoplasmic mislocalization, aggregation, and co-aggregation of TDP-43, FUS, and SOD1 can be identified as proteinopathies akin to other neurodegenerative diseases (NDs), eliciting strong ties to disrupted RNA splicing, transport, and stability. In recent years, microRNAs (miRNAs) have also been increasingly implicated in the disease, and are of greater significance as they are the master regulators of RNA metabolism in disease pathology. However, little is known about the role of these proteins and how they are regulated by miRNA, which would provide mechanistic insights into ALS pathogenesis. This review seeks to discuss current developments across TDP-43, FUS, and SOD1 to build a detailed snapshot of the network pathophysiology underlying ALS while aiming to highlight possible novel therapeutic targets to guide future research.

BraInMap Elucidates the Macromolecular Connectivity Landscape of Mammalian Brain

Connectivity webs mediate the unique biology of the mammalian brain. Yet, while cell circuit maps are increasingly available, knowledge of their underlying molecular networks remains limited. Here, we applied multi-dimensional biochemical fractionation with mass spectrometry and machine learning to survey endogenous macromolecules across the adult mouse brain. We defined a global "interactome" comprising over one thousand multi-protein complexes. These include hundreds of brain-selective assemblies that have distinct physical and functional attributes, show regional and cell-type specificity, and have links to core neurological processes and disorders. Using reciprocal pull-downs and a transgenic model, we validated a putative 28-member RNA-binding protein complex associated with amyotrophic lateral sclerosis, suggesting a coordinated function in alternative splicing in disease progression. This brain interaction map (BraInMap) resource facilitates mechanistic exploration of the unique molecular machinery driving core cellular processes of the central nervous system. It is publicly available and can be explored here https://www.bu.edu/dbin/cnsb/mousebrain/.

Multifaceted roles of microRNAs: From motor neuron generation in embryos to degeneration in spinal muscular atrophy

Two crucial questions in neuroscience are how neurons establish individual identity in the developing nervous system and why only specific neuron subtypes are vulnerable to neurodegenerative diseases. In the central nervous system, spinal motor neurons serve as one of the best-characterized cell types for addressing these two questions. In this review, we dissect these questions by evaluating the emerging role of regulatory microRNAs in motor neuron generation in developing embryos and their potential contributions to neurodegenerative diseases such as spinal muscular atrophy (SMA). Given recent promising results from novel microRNA-based medicines, we discuss the potential applications of microRNAs for clinical assessments of SMA disease progression and treatment.

Disruption of RNA Metabolism in Neurological Diseases and Emerging Therapeutic Interventions

RNA binding proteins are critical to the maintenance of the transcriptome via controlled regulation of RNA processing and transport. Alterations of these proteins impact multiple steps of the RNA life cycle resulting in various molecular phenotypes such as aberrant RNA splicing, transport, and stability. Disruption of RNA binding proteins and widespread RNA processing defects are increasingly recognized as critical determinants of neurological diseases. Here, we describe distinct mechanisms by which the homeostasis of RNA binding proteins is compromised in neurological disorders through their reduced expression level, increased propensity to aggregate or sequestration by abnormal RNAs. These mechanisms all converge toward altered neuronal function highlighting the susceptibility of neurons to deleterious changes in RNA expression and the central role of RNA binding proteins in preserving neuronal integrity. Emerging therapeutic approaches to mitigate or reverse alterations of RNA binding proteins in neurological diseases are discussed.

Mir-17∼92 Confers Motor Neuron Subtype Differential Resistance to ALS-Associated Degeneration

Progressive degeneration of motor neurons (MNs) is the hallmark of amyotrophic lateral sclerosis (ALS). Limb-innervating lateral motor column MNs (LMC-MNs) seem to be particularly vulnerable and are among the first MNs affected in ALS. Here, we report association of this differential susceptibility with reduced expression of the mir-17∼92 cluster in LMC-MNs prior to disease onset. Reduced mir-17∼92 is accompanied by elevated nuclear PTEN in spinal MNs of presymptomatic SOD1^G93A mice. Selective dysregulation of the mir-17∼92/nuclear PTEN axis in degenerating SOD1^G93A LMC-MNs was confirmed in a double-transgenic embryonic stem cell system and recapitulated in human SOD1^+/L144F-induced pluripotent stem cell (iPSC)-derived MNs. We further show that overexpression of mir-17∼92 significantly rescues human SOD1^+/L144F MNs, and intrathecal delivery of adeno-associated virus (AAV)9-mir-17∼92 improves motor deficits and survival in SOD1^G93A mice. Thus, mir-17∼92 may have value as a prognostic marker of MN degeneration and is a candidate therapeutic target in SOD1-linked ALS. VIDEO ABSTRACT.

RNA Dysregulation in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motor neuron disease and is characterized by the degeneration of upper and lower motor neurons. It has become increasingly clear that RNA dysregulation is a key contributor to ALS pathogenesis. The major ALS genes SOD1, TARDBP, FUS, and C9orf72 are involved in aspects of RNA metabolism processes such as mRNA transcription, alternative splicing, RNA transport, mRNA stabilization, and miRNA biogenesis. In this review, we highlight the current understanding of RNA dysregulation in ALS pathogenesis involving these major ALS genes and discuss the potential of therapeutic strategies targeting disease RNAs for treating ALS.

Protective paraspeckle hyper-assembly downstream of TDP-43 loss of function in amyotrophic lateral sclerosis

BACKGROUND

Paraspeckles are subnuclear bodies assembled on a long non-coding RNA (lncRNA) NEAT1. Their enhanced formation in spinal neurons of sporadic amyotrophic lateral sclerosis (ALS) patients has been reported but underlying mechanisms are unknown. The majority of ALS cases are characterized by TDP-43 proteinopathy. In current study we aimed to establish whether and how TDP-43 pathology may augment paraspeckle assembly.

METHODS

Paraspeckle formation in human samples was analysed by RNA-FISH and laser capture microdissection followed by qRT-PCR. Mechanistic studies were performed in stable cell lines, mouse primary neurons and human embryonic stem cell-derived neurons. Loss and gain of function for TDP-43 and other microRNA pathway factors were modelled by siRNA-mediated knockdown and protein overexpression.

RESULTS

We show that de novo paraspeckle assembly in spinal neurons and glial cells is a hallmark of both sporadic and familial ALS with TDP-43 pathology. Mechanistically, loss of TDP-43 but not its cytoplasmic accumulation or aggregation augments paraspeckle assembly in cultured cells. TDP-43 is a component of the microRNA machinery, and recently, paraspeckles have been shown to regulate pri-miRNA processing. Consistently, downregulation of core protein components of the miRNA pathway also promotes paraspeckle assembly. In addition, depletion of these proteins or TDP-43 results in accumulation of endogenous dsRNA and activation of type I interferon response which also stimulates paraspeckle formation. We demonstrate that human or mouse neurons in vitro lack paraspeckles, but a synthetic dsRNA is able to trigger their de novo formation. Finally, paraspeckles are protective in cells with compromised microRNA/dsRNA metabolism, and their assembly can be promoted by a small-molecule microRNA enhancer.

CONCLUSIONS

Our study establishes possible mechanisms behind paraspeckle hyper-assembly in ALS and suggests their utility as therapeutic targets in ALS and other diseases with abnormal metabolism of microRNA and dsRNA.

miRNA targeting and alternative splicing in the stress response - events hosted by membrane-less compartments

Stress can be temporary or chronic, and mild or acute. Depending on its extent and severity, cells either alter their metabolism, and adopt a new state, or die. Fluctuations in environmental conditions occur frequently, and such stress disturbs cellular homeostasis, but in general, stresses are reversible and last only a short time. There is increasing evidence that regulation of gene expression in response to temporal stress happens post-transcriptionally in specialized subcellular membrane-less compartments called ribonucleoprotein (RNP) granules. RNP granules assemble through a concentration-dependent liquid-liquid phase separation of RNA-binding proteins that contain low-complexity sequence domains (LCDs). Interestingly, many factors that regulate microRNA (miRNA) biogenesis and alternative splicing are RNA-binding proteins that contain LCDs and localize to stress-induced liquid-like compartments. Consequently, gene silencing through miRNAs and alternative splicing of pre-mRNAs are emerging as crucial post-transcriptional mechanisms that function on a genome-wide scale to regulate the cellular stress response. In this Review, we describe the interplay between these two post-transcriptional processes that occur in liquid-like compartments as an adaptive cellular response to stress.

Lost in Translation: Evidence for Protein Synthesis Deficits in ALS/FTD and Related Neurodegenerative Diseases

Cells utilize a complex network of proteins to regulate translation, involving post-transcriptional processing of RNA and assembly of the ribosomal unit. Although the complexity provides robust regulation of proteostasis, it also offers several opportunities for translational dysregulation, as has been observed in many neurodegenerative disorders. Defective mRNA localization, mRNA sequatration, inhibited ribogenesis, mutant tRNA synthetases, and translation of hexanucleotide expansions have all been associated with neurodegenerative disease. Here, we review dysregulation of translation in the context of age-related neurodegeneration and discuss novel methods to interrogate translation. This review primarily focuses on amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), a spectrum disorder heavily associated with RNA metabolism, while also analyzing translational inhibition in the context of related neurodegenerative disorders such as Alzheimer's disease and Huntington's disease and the translation-related pathomechanisms common in neurodegenerative disease.

A missense MT-ND5 mutation in differentiated Parkinson Disease cytoplasmic hybrid induces ROS-dependent DNA Damage Response amplified by DROSHA

Genome integrity is continuously threatened by endogenous sources of DNA damage including reactive oxygen species (ROS) produced by cell metabolism. Factors of the RNA interference (RNAi) machinery have been recently involved in the cellular response to DNA damage (DDR) in proliferating cells. To investigate the impact of component of RNAi machinery on DDR activation in terminally differentiated cells, we exploited cytoplasmic hybrid (cybrid) cell lines in which mitochondria of sporadic Parkinson’s disease patients repopulate neuroblastoma SH-SY5Y-Rho(0) cells. Upon differentiation into dopaminergic neuron-like cells, PD63 cybrid showed increased intracellular level of ROS and chronic DDR activation, compared to other cybrids with the same nuclear background. Importantly, DDR activation in these cells can be prevented by ROS scavenging treatment suggesting that ROS production is indeed causative of nuclear DNA damage. Sequence analysis of the mitogenomes identified a rare and heteroplasmic missense mutation affecting a highly conserved residue of the ND5-subunit of respiratory complex I, which accounts for ROS increase. We demonstrated that the assembly of nuclear DDR foci elicited by oxidative stress in these cells relies on DROSHA, providing the first evidence that components of RNAi machinery play a crucial role also in the mounting of ROS-induced DDR in non-replicating neuronal cells.

Imaging and fluid biomarkers in frontotemporal dementia

Frontotemporal dementia (FTD), the second most common type of presenile dementia, is a heterogeneous neurodegenerative disease characterized by progressive behavioural and/or language problems, and includes a range of clinical, genetic and pathological subtypes. The diagnostic process is hampered by this heterogeneity, and correct diagnosis is becoming increasingly important to enable future clinical trials of disease-modifying treatments. Reliable biomarkers will enable us to better discriminate between FTD and other forms of dementia and to predict disease progression in the clinical setting. Given that different underlying pathologies probably require specific pharmacological interventions, robust biomarkers are essential for the selection of patients with specific FTD subtypes. This Review emphasizes the increasing availability and potential applications of structural and functional imaging biomarkers, and cerebrospinal fluid and blood fluid biomarkers in sporadic and genetic FTD. The relevance of new MRI modalities - such as voxel-based morphometry, diffusion tensor imaging and arterial spin labelling - in the early stages of FTD is discussed, together with the ability of these modalities to classify FTD subtypes. We highlight promising new fluid biomarkers for staging and monitoring of FTD, and underline the importance of large, multicentre studies of individuals with presymptomatic FTD. Harmonization in the collection and analysis of data across different centres is crucial for the implementation of new biomarkers in clinical practice, and will become a great challenge in the next few years.

Peptidylarginine Deiminases-Roles in Cancer and Neurodegeneration and Possible Avenues for Therapeutic Intervention via Modulation of Exosome and Microvesicle (EMV) Release?

Exosomes and microvesicles (EMVs) are lipid bilayer-enclosed structures released from cells and participate in cell-to-cell communication via transport of biological molecules. EMVs play important roles in various pathologies, including cancer and neurodegeneration. The regulation of EMV biogenesis is thus of great importance and novel ways for manipulating their release from cells have recently been highlighted. One of the pathways involved in EMV shedding is driven by peptidylarginine deiminase (PAD) mediated post-translational protein deimination, which is calcium-dependent and affects cytoskeletal rearrangement amongst other things. Increased PAD expression is observed in various cancers and neurodegeneration and may contribute to increased EMV shedding and disease progression. Here, we review the roles of PADs and EMVs in cancer and neurodegeneration.

Fluid-Based Biomarkers for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a highly heterogeneous disease with no effective treatment. Drug development has been hampered by the lack of biomarkers that aid in early diagnosis, demonstrate target engagement, monitor disease progression, and can serve as surrogate endpoints to assess the efficacy of treatments. Fluid-based biomarkers may potentially address these issues. An ideal biomarker should exhibit high specificity and sensitivity for distinguishing ALS from control (appropriate disease mimics and other neurologic diseases) populations and monitor disease progression within individual patients. Significant progress has been made using cerebrospinal fluid, serum, and plasma in the search for ALS biomarkers, with urine and saliva biomarkers still in earlier stages of development. A few of these biomarker candidates have demonstrated use in patient stratification, predicting disease course (fast vs slow progression) and severity, or have been used in preclinical and clinical applications. However, while ALS biomarker discovery has seen tremendous advancements in the last decade, validating biomarkers and moving them towards the clinic remains more elusive. In this review, we highlight biomarkers that are moving towards clinical utility and the challenges that remain in order to implement biomarkers at all stages of the ALS drug development process.

Identification of miRNAs as Potential Biomarkers in Cerebrospinal Fluid from Amyotrophic Lateral Sclerosis Patients

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal neurodegenerative disorder. Since no diagnostic laboratory test exists, the identification of specific biomarkers could be fundamental in clinical practice. microRNAs (miRNAs) are considered promising biomarkers for neurodegenerative diseases. The aim of the study was to identify a CSF miRNA set that could differentiate ALS from non-ALS condition. miRNA profiling in CSF from ALS patients (n = 24; eight with C9orf72 expansion) and unaffected control subjects (n = 24) by quantitative reverse transcription PCR identified fourteen deregulated miRNAs. Validation experiments confirmed eight miRNAs as significantly deregulated in ALS. No significant differences were observed between ALS patients with or without C9orf72 expansion. The receiver operator characteristic (ROC) curve analyses revealed the highest diagnostic accuracy for the upregulated miR181a-5p and the downregulated miR21-5p and miR15b-5p. The miR181a-5p/miR21-5p and miR181a-5p/miR15b-5p ratios detected ALS with 90 and 85 % sensitivity and 87 and 91 % specificity, respectively, confirming the application potential as disease biomarkers. These deregulated miRNAs are implicated in apoptotic way and provide insight into processes responsible for motor neuron degeneration.