Amyotrophic lateral sclerosis and non-tau frontotemporal lobar degeneration

Amplifying the Heat Shock Response Ameliorates ALS and FTD Pathology in Mouse and Human Models

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are now known as parts of a disease spectrum with common pathological features and genetic causes. However, as both conditions are clinically heterogeneous, patient groups may be phenotypically similar but pathogenically and genetically variable. Despite numerous clinical trials, there remains no effective therapy for these conditions, which, in part, may be due to challenges of therapy development in a heterogeneous patient population. Disruption to protein homeostasis is a key feature of different forms of ALS and FTD. Targeting the endogenous protein chaperone system, the heat shock response (HSR) may, therefore, be a potential therapeutic approach. We conducted a preclinical study of a known pharmacological amplifier of the HSR, called arimoclomol, in mice with a mutation in valosin-containing protein (VCP) which causes both ALS and FTD in patients. We demonstrate that amplification of the HSR ameliorates the ALS/FTD-like phenotype in the spinal cord and brain of mutant VCP mice and prevents neuronal loss, replicating our earlier findings in the SOD1 mouse model of ALS. Moreover, in human cell models, we demonstrate improvements in pathology upon arimoclomol treatment in mutant VCP patient fibroblasts and iPSC-derived motor neurons. Our findings suggest that targeting of the HSR may have therapeutic potential, not only in non-SOD1 ALS, but also for the treatment of FTD.

RNA-binding proteins in degenerative joint diseases: A systematic review

RNA-binding proteins (RBPs), which are conserved proteins comprising multiple intermediate sequences, can interact with proteins, messenger RNA (mRNA) of coding genes, and non-coding RNAs to perform different biological functions, such as the regulation of mRNA stability, selective polyadenylation, and the management of non-coding microRNA (miRNA) synthesis to affect downstream targets. This article will highlight the functions of RBPs, in degenerative joint diseases (intervertebral disc degeneration [IVDD] and osteoarthritis [OA]). It will reviews the latest advancements on the regulatory mechanism of RBPs in degenerative joint diseases, in order to understand the pathophysiology, early diagnosis and treatment of OA and IVDD from a new perspective.

The CXCL12/CXCR4/ACKR3 Response Axis in Chronic Neurodegenerative Disorders of the Central Nervous System: Therapeutic Target and Biomarker

There has been an increase in the incidence of chronic neurodegenerative disorders of the central nervous system, including Alzheimer's and Parkinson's diseases, over the recent years mostly due to the rise in the number of elderly individuals. In addition, various neurodegenerative disorders are related to imbalances in the CXCL12/CXCR4/ACKR3 response axis. Notably, the CXC Chemokine Ligand 12 (CXCL12) is essential for the development of the central nervous system. Moreover, the expression and distribution of CXCL12 and its receptors are associated with the aggravation or alleviation of symptoms of neurodegenerative disorders. Therefore, the current review sought to highlight the specific functions of CXCL12 and its receptors in various neurodegenerative disorders, in order to provide new insights for future research.

TDP-43 promotes tau accumulation and selective neurotoxicity in bigenic Caenorhabditis elegans

Although amyloid β (Aβ) and tau aggregates define the neuropathology of Alzheimer's disease (AD), TDP-43 has recently emerged as a co-morbid pathology in more than half of patients with AD. Individuals with concomitant Aβ, tau and TDP-43 pathology experience accelerated cognitive decline and worsened brain atrophy, but the molecular mechanisms of TDP-43 neurotoxicity in AD are unknown. Synergistic interactions among Aβ, tau and TDP-43 may be responsible for worsened disease outcomes. To study the biology underlying this process, we have developed new models of protein co-morbidity using the simple animal Caenorhabditis elegans. We demonstrate that TDP-43 specifically enhances tau but not Aβ neurotoxicity, resulting in neuronal dysfunction, pathological tau accumulation and selective neurodegeneration. Furthermore, we find that synergism between tau and TDP-43 is rescued by loss-of-function of the robust tau modifier sut-2. Our results implicate enhanced tau neurotoxicity as the primary driver underlying worsened clinical and neuropathological phenotypes in AD with TDP-43 pathology, and identify cell-type specific sensitivities to co-morbid tau and TDP-43. Determining the relationship between co-morbid TDP-43 and tau is crucial to understand, and ultimately treat, mixed pathology AD.

Amyotrophic lateral sclerosis and delayed onset muscle soreness in light of the impaired blink and stretch reflexes – watch out for Piezo2

Amyotrophic lateral sclerosis (ALS) is a fatal, multisystem neurodegenerative disease that causes the death of motoneurons (MNs) progressively and eventually leads to paralysis. In contrast, delayed onset muscle soreness (DOMS) is defined as delayed onset soreness, muscle stiffness, loss of force-generating capacity, reduced joint range of motion, and decreased proprioceptive function. Sensory deficits and impaired proprioception are common symptoms of both ALS and DOMS, as impairment at the proprioceptive sensory terminals in the muscle spindle is theorized to occur in both. The important clinical distinction is that extraocular muscles (EOM) are relatively spared in ALS, in contrast to limb skeletal muscles; however, the blink reflex goes through a gradual impairment in a later stage of disease progression. Noteworthy is, that, the stretch of EOM induces the blink reflex. The current authors suggest that the impairment of proprioceptive sensory nerve terminals in the EOM muscle spindles are partially responsible for lower blink reflex, beyond central origin, and implies the critical role of Piezo2 ion channels and Wnt-PIP2 signaling in this pathomechanism. The proposed microinjury of Piezo2 on muscle spindle proprioceptive terminals could provide an explanation for the painless dying-back noncontact injury mechanism theory of ALS.

Nuclear lipidome is altered in amyotrophic lateral sclerosis: A pilot study

Nucleocytosolic transport, a membrane process, is impaired in motor neurons in amyotrophic lateral sclerosis (ALS). This study analyzes the nuclear lipidome in motor neurons in ALS and examines molecular pathways linked to the major lipid alterations. Nuclei were obtained from the frozen anterior horn of the lumbar spinal cord of ALS patients and age-matched controls. Lipidomic profiles of this subcellular fraction were obtained using liquid chromatography and mass spectrometry. We validated the mechanisms behind presumable lipidomic changes by exploring ALS surrogate models including human motor neurons (derived from ALS lines and controls) subjected to oxidative stress, the hSOD-G93A transgenic mice, and samples from an independent cohort of ALS patients. Among the differential lipid species, we noted 41 potential identities, mostly belonging to phospholipids (particularly ether phospholipids, as plasmalogens), as well as diacylglycerols and triacylglycerides. Decreased expression of alkyldihydroxyacetonephosphate synthase (AGPS)-a critical peroxisomal enzyme in plasmalogen synthesis-is found in motor neuron disease models; this occurs in parallel with an increase in the expression of sterol carrier protein 2 (SCP2) mRNA in ALS and Scp2 levels in G93A transgenic mice. Further, we identified diminished expression of diacylglycerol-related enzymes, such as phospholipase C βI (PLCβI) and protein kinase CβII (PKCβII), linked to diacylglycerol metabolism. Finally, lipid droplets were recognized in the nuclei, supporting the identification of triacylglycerides as differential lipids. Our results point to the potentially pathogenic role of altered composition of nuclear membrane lipids and lipids in the nucleoplasm in the anterior horn of the spinal cord in ALS. Overall, these data support the usefulness of subcellular lipidomics applied to neurodegenerative diseases.

RNA packaging into extracellular vesicles: An orchestra of RNA-binding proteins?

Extracellular vesicles (EVs) are heterogeneous membranous particles released from the cells through different biogenetic and secretory mechanisms. We now conceive EVs as shuttles mediating cellular communication, carrying a variety of molecules resulting from intracellular homeostatic mechanisms. The RNA is a widely detected cargo and, impressively, a recognized functional intermediate that elects EVs as modulators of cancer cell phenotypes, determinants of disease spreading, cell surrogates in regenerative medicine, and a source for non-invasive molecular diagnostics. The mechanistic elucidation of the intracellular events responsible for the engagement of RNA into EVs will significantly improve the comprehension and possibly the prediction of EV "quality" in association with cell physiology. Interestingly, the application of multidisciplinary approaches, including biochemical as well as cell-based and computational strategies, is increasingly revealing an active RNA-packaging process implicating RNA-binding proteins (RBPs) in the sorting of coding and non-coding RNAs. In this review, we provide a comprehensive view of RBPs recently emerging as part of the EV biology, considering the scenarios where: (i) individual RBPs were detected in EVs along with their RNA substrates, (ii) RBPs were detected in EVs with inferred RNA targets, and (iii) EV-transcripts were found to harbour sequence motifs mirroring the activity of RBPs. Proteins so far identified are members of the hnRNP family (hnRNPA2B1, hnRNPC1, hnRNPG, hnRNPH1, hnRNPK, and hnRNPQ), as well as YBX1, HuR, AGO2, IGF2BP1, MEX3C, ANXA2, ALIX, NCL, FUS, TDP-43, MVP, LIN28, SRP9/14, QKI, and TERT. We describe the RBPs based on protein domain features, current knowledge on the association with human diseases, recognition of RNA consensus motifs, and the need to clarify the functional significance in different cellular contexts. We also summarize data on previously identified RBP inhibitor small molecules that could also be introduced in EV research as potential modulators of vesicular RNA sorting.

Effects of exercise on sleep in neurodegenerative disease

As the population ages, the incidence and prevalence of neurodegenerative disorders will continue to increase. Persons with neurodegenerative disease frequently experience sleep disorders, which not only affect quality of life, but potentially accelerate progression of the disease. Unfortunately, pharmacological interventions are often futile or have adverse effects. Therefore, investigation of non-pharmacological interventions has the potential to expand the treatment landscape for these disorders. The last decade has observed increasing recognition of the beneficial role of exercise in brain diseases, and neurodegenerative disorders in particular. In this review, we will focus on the therapeutic role of exercise for sleep dysfunction in four neurodegenerative diseases, namely Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Available data suggest that exercise may have the potential to improve sleep disorders and attenuate neurodegeneration, particularly in Alzheimer's disease and Parkinson's disease. However, additional research is required in order to understand the most effective exercise therapy for these indications; the best way to monitor the response to interventions; the influence of exercise on sleep dysfunction in Huntington's disease and amyotrophic lateral sclerosis; and the mechanisms underlying exercise-induced sleep modifications.

Assessing circular RNAs in Alzheimer's disease and frontotemporal lobar degeneration

A circular-transcriptome-wide study has recently linked differential expression of circular RNAs (circRNAs) in brain tissue with Alzheimer's disease (AD). We aimed at replicating the major findings in an independent series of sporadic and familial AD. We also included cases with frontotemporal lobar degeneration (FTLD), comprising brain specimens with TDP-43 aggregates (FTLD-TDP43) and samples that presented Tau accumulation (FTLD-Tau). Using a quantitative polymerase chain reaction approach, we evaluated 8 circRNAs that surpassed the significant threshold in the former meta-analysis (circHOMER1, circDOCK1, circFMN1, circKCNN2, circRTN4, circMAN2A1, circMAP7, and circPICALM). Average expression changes between patients with AD and controls followed the same directions as previously reported. We also confirmed an exacerbated alteration in circRNA expression in the familial AD group compared with the sporadic forms. Two circRNAs (circHOMER1 and circKCNN2) also showed significant expression alterations in the group of FTLD-Tau and FTLD-TDP43, respectively. Overall, these results reinforce the conception that expression of circRNAs is different in AD, and also suggest a wider involvement of this particular class of RNA in other neurodegenerative dementias.

Are comorbidities compatible with a molecular pathological classification of neurodegenerative diseases?

PURPOSE OF REVIEW

The purpose of this review is to provide an update on comorbidities in neurodegenerative conditions. The term comorbidity is used here to distinguish cases with overlapping pathogenic mechanisms, which includes combinations of neurodegenerative proteinopathies from cases with multimorbidity, which is defined as concomitant brain and systemic disorders with different pathogenic mechanisms.

RECENT FINDINGS

Comorbid proteinopathies are more frequent in both sporadic and hereditary neurodegenerative diseases than previously assumed. The most frequent additional proteinopathies are related to Alzheimer's disease, Lewy body disorder, and limbic predominant transactive response DNA-binding protein 43 proteinopathy, however, different forms of tau pathologies are also increasingly recognized. In addition to ageing, synergistic interaction of proteins, common disease pathways, and the influence of genetic variations are discussed as possible pathogenic players.

SUMMARY

Comorbid proteinopathies might influence the clinical course and have implications for biomarker and therapeutic development. As pure forms of proteinopathies are still observed, the notion of current molecular classification is justified. This corroborates elucidation of various pathogenic pathways leading to neurodegeneration. Assuming that single proteins and associated pathways are targeted in therapy trials, efforts are needed to better stratify patients and to select pure proteinopathy forms lacking unfavorable genetic constellations. Otherwise combined therapeutic strategies might be necessary for comorbid proteinopathies.

Inherited and Sporadic Amyotrophic Lateral Sclerosis and Fronto-Temporal Lobar Degenerations arising from Pathological Condensates of Phase Separating Proteins

Recent work on the biophysics of proteins with low complexity, intrinsically disordered domains that have the capacity to form biological condensates has profoundly altered the concepts about the pathogenesis of inherited and sporadic neurodegenerative disorders associated with pathological accumulation of these proteins. In the present review, we use the FUS, TDP-43 and A11 proteins as examples to illustrate how missense mutations and aberrant post-translational modifications of these proteins cause amyotrophic lateral sclerosis (ALS) and fronto-temporal lobar degeneration (FTLD).

Longitudinal RNA-Seq analysis of acute and chronic neurogenic skeletal muscle atrophy

Skeletal muscle is a highly adaptable tissue capable of changes in size, contractility, and metabolism according to functional demands. Atrophy is a decline in mass and strength caused by pathologic loss of myofibrillar proteins, and can result from disuse, aging, or denervation caused by injury or peripheral nerve disorders. We provide a high-quality longitudinal RNA-Seq dataset of skeletal muscle from a cohort of adult C57BL/6J male mice subjected to tibial nerve denervation for 0 (baseline), 1, 3, 7, 14, 30, or 90 days. Using an unbiased genomics approach to identify gene expression changes across the entire longitudinal course of muscle atrophy affords the opportunity to (1) establish acute responses to denervation, (2) detect pathways that mediate rapid loss of muscle mass within the first week after denervation, and (3) capture the molecular phenotype of chronically atrophied muscle at a stage when it is largely resistant to recovery.

Sleep disturbances in patients with amyotrophic lateral sclerosis: current perspectives

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease inevitably leading to generalized muscle weakness and premature death. Sleep disturbances are extremely common in patients with ALS and substantially add to the burden of disease for both patients and caregivers. Disruption of sleep can be caused by physical symptoms, such as muscle cramps, pain, reduced mobility, spasticity, mucus retention, and restless legs syndrome. In addition, depression and anxiety may lead to significant insomnia. In a small subset of patients, rapid eye movement (REM) sleep behavioral disorder may be present, reflecting neurodegeneration of central nervous system pathways which are involved in REM sleep regulation. With regard to overall prognosis, sleep-disordered breathing (SDB) and nocturnal hypoventilation (NH) are of utmost importance, particularly because NH precedes respiratory failure. Timely mechanical ventilation is one of the most significant therapeutic measures to prolong life span in ALS, and transcutaneous capnometry is superior to pulse oxymetry to detect NH early. In addition, it has been shown that in patients on home ventilatory support, survival time depends on whether normocapnia, normoxia, and elimination of apneic events during sleep can be reliably achieved. Several studies have investigated sleep patterns and clinical determinants of sleep disruption in ALS, but exact prevalence numbers are unknown. Thus, constant awareness for sleep-related symptoms is appropriate. Since no curative treatment can be offered to affected patients, sleep complaints should be thoroughly investigated in order to identify any treatable etiology and improve or stabilize quality of life as much as possible. The use of hypnotics should be confined to palliation during the terminal phase and refractory insomnia in earlier stages of the disease, taking into account that most compounds potentially aggravate SDB.

Molecular Mechanisms of Neurodegeneration Related to C9orf72 Hexanucleotide Repeat Expansion

Two clinically distinct diseases, amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), have recently been classified as two extremes of the FTD/ALS spectrum. The neuropathological correlate of FTD is frontotemporal lobar degeneration (FTLD), characterized by tau-, TDP-43-, and FUS-immunoreactive neuronal inclusions. An earlier discovery that a hexanucleotide repeat expansion mutation in chromosome 9 open reading frame 72 (C9orf72) gene causes ALS and FTD established a special subtype of ALS and FTLD with TDP-43 pathology (C9FTD/ALS). Normal individuals carry 2–10 hexanucleotide GGGGCC repeats in the C9orf72 gene, while more than a few hundred repeats represent a risk for ALS and FTD. The proposed molecular mechanisms by which C9orf72 repeat expansions induce neurodegenerative changes are C9orf72 loss-of-function through haploinsufficiency, RNA toxic gain-of-function, and gain-of-function through the accumulation of toxic dipeptide repeat proteins. However, many more cellular processes are affected by pathological processes in C9FTD/ALS, including nucleocytoplasmic transport, RNA processing, normal function of nucleolus, formation of membraneless organelles, translation, ubiquitin proteasome system, Notch signalling pathway, granule transport, and normal function of TAR DNA-binding protein 43 (TDP-43). Although the exact molecular mechanisms through which C9orf72 repeat expansions account for neurodegeneration have not been elucidated, some potential therapeutics, such as antisense oligonucleotides targeting hexanucleotide GGGGCC repeats in mRNA, were successful in preclinical trials and are awaiting phase 1 clinical trials. In this review, we critically discuss each proposed mechanism and provide insight into the most recent studies aiming to elucidate the molecular underpinnings of C9FTD/ALS.

Biomarkers for diseases with TDP-43 pathology

The discovery that aggregated transactive response DNA-binding protein 43 kDa (TDP-43) is the major component of pathological ubiquitinated inclusions in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) caused seminal progress in the unveiling of the genetic bases and molecular characteristics of these now so-called TDP-43 proteinopathies. Substantial increase in the knowledge of clinic-pathological coherencies, especially for FTLD variants, could be made in the last decade, but also revealed a considerable complexity of TDP-43 pathology and often a poor correlation of clinical and molecular disease characteristics. To date, an underlying TDP-43 pathology can be predicted only for patients with mutations in the genes C9orf72 and GRN, but is dependent on neuropathological verification in patients without family history, which represent the majority of cases. As etiology-specific therapies for neurodegenerative proteinopathies are emerging, methods to forecast TDP-43 pathology at patients' lifetime are highly required. Here, we review the current status of research pursued to identify specific indicators to predict or exclude TDP-43 pathology in the ALS-FTLD spectrum disorders and findings on candidates for prognosis and monitoring of disease progression in TDP-43 proteinopathies with a focus on TDP-43 with its pathological forms, neurochemical and imaging biomarkers.

The physiological and pathological biophysics of phase separation and gelation of RNA binding proteins in amyotrophic lateral sclerosis and fronto-temporal lobar degeneration

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Some intrinsically disordered proteins undergo reversible phase separation/gelation.

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Reversible phase separation/gelation underpins function of membraneless organelles.

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fALS-FUS mutations increase propensity of FUS to form highly stable condensates.

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Changes in arginine methylation and FUS chaperones in FTLD-FUS have similar effects.

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Stable fibrillar condensates sequester cargo and impair RNP granule function.

Many RNA binding proteins, including FUS, contain moderately repetitive, low complexity, intrinsically disordered domains. These sequence motifs have recently been found to underpin reversible liquid: liquid phase separation and gelation of these proteins, permitting them to reversibly transition from a monodispersed state to liquid droplet- or hydrogel-like states. This function allows the proteins to serve as scaffolds for the formation of reversible membraneless intracellular organelles such as nucleoli, stress granules and neuronal transport granules. Using FUS as an example, this review examines the biophysics of this physiological process, and reports on how mutations and changes in post-translational state alter phase behaviour, and lead to neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal lobar degeneration.