Molecular Mechanisms of TDP-43 Misfolding and Pathology in Amyotrophic Lateral Sclerosis

Role of Oxidative Stress on the Etiology and Pathophysiology of Amyotrophic Lateral Sclerosis (ALS) and Its Relation with the Enteric Nervous System

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease affecting motor neurons in the spinal cord, cerebral cortex, and medulla oblongata. Most patients present a clinical phenotype of classic ALS-with predominant atrophy, muscle weakness, and fasciculations-and survival of 3 to 5 years following diagnosis. In the present review, we performed a literature search to provide an update on the etiology and pathophysiological mechanisms involved in ALS. There are two types of ALS: the familial form with genetic involvement, and the sporadic form with a multifactorial origin. ALS pathophysiology is characterized by involvement of multiple processes, including oxidative stress, glutamate excitotoxicity, and neuroinflammation. Moreover, it is proposed that conditioning risk factors affect ALS development, such as susceptibility to neurodegeneration in motor neurons, the intensity of performed physical activity, and intestinal dysbiosis with involvement of the enteric nervous system, which supports the existing theories of disease generation. To improve patients' prognosis and survival, it is necessary to further deepen our understanding of the etiopathogenesis of ALS.

Enhanced axonal regeneration of ALS patient iPSC-derived motor neurons harboring SOD1A4V mutation

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease, characterized by degeneration of upper and lower motor neurons that leads to muscle weakness, paralysis, and death, but the effects of disease-causing mutations on axonal outgrowth of neurons derived from human induced pluripotent stem cells (iPSC)-derived motor neurons (hiPSC-MN) are poorly understood. The use of hiPSC-MN is a promising tool to develop more relevant models for target identification and drug development in ALS research, but questions remain concerning the effects of distinct disease-causing mutations on axon regeneration. Mutations in superoxide dismutase 1 (SOD1) were the first to be discovered in ALS patients. Here, we investigated the effect of the SOD1A4V mutation on axonal regeneration of hiPSC-MNs, utilizing compartmentalized microfluidic devices, which are powerful tools for studying hiPSC-MN distal axons. Surprisingly, SOD1+/A4V hiPSC-MNs regenerated axons more quickly following axotomy than those expressing the native form of SOD1. Though initial axon regrowth was not significantly different following axotomy, enhanced regeneration was apparent at later time points, indicating an increased rate of outgrowth. This regeneration model could be used to identify factors that enhance the rate of human axon regeneration.

Shapeshifter TDP-43: Molecular mechanism of structural polymorphism, aggregation, phase separation and their modulators

TDP-43 is a nucleic acid-binding protein that performs physiologically essential functions and is known to undergo phase separation and aggregation during stress. Initial observations have shown that TDP-43 forms heterogeneous assemblies, including monomer, dimer, oligomers, aggregates, phase-separated assemblies, etc. However, the significance of each assembly of TDP-43 concerning its function, phase separation, and aggregation is poorly known. Furthermore, how different assemblies of TDP-43 are related to each other is unclear. In this review, we focus on the various assemblies of TDP-43 and discuss the plausible origin of the structural heterogeneity of TDP-43. TDP-43 is involved in multiple physiological processes like phase separation, aggregation, prion-like seeding, and performing physiological functions. However, the molecular mechanism behind the physiological process performed by TDP-43 is not well understood. The current review discusses the plausible molecular mechanism of phase separation, aggregation, and prion-like propagation of TDP-43.

Immunization with Neural-Derived Peptides in Neurodegenerative Diseases: A Narrative Review

Neurodegenerative diseases (NDDs) are a major health problem worldwide. Statistics suggest that in America in 2030 there will be more than 12 million people suffering from a neurodegenerative pathology. Furthermore, the increase in life expectancy enhances the importance of finding new and better therapies for these pathologies. NDDs could be classified into chronic or acute, depending on the time required for the development of clinical symptoms and brain degeneration. Nevertheless, both chronic and acute stages share a common immune and inflammatory pathway in their pathophysiology. Immunization with neural-derived peptides (INDP) is a novel therapy that has been studied during the last decade. By inoculating neural-derived peptides obtained from the central nervous system (CNS), this therapy aims to boost protective autoimmunity, an autoreactive response that leads to a protective phenotype that produces a healing environment and neuroregeneration instead of causing damage. INDP has shown promising findings in studies performed either in vitro, in vivo or even in some pre-clinical trials of different NDDs, standing as a potentially beneficial therapy. In this review, we will describe some of the studies in which the effect of INDP strategies have been explored in different (chronic and acute) neurodegenerative diseases.

Biophysical evaluation of the oligomerization and conformational properties of the N-terminal domain of TDP-43

TDP-43 is an RNA-binding protein that presents four domains comprising an N-terminal region, two RNA recognition motifs and a C-terminal region. The N-terminal domain (NTD) has a relevant role in the oligomerization and splicing activity of TDP-43. In this work, we have expressed, purified and biophysically characterized the region that includes residues 1 to 102 that contains the nuclear localization signal (residues 80-102, NLS). Furthermore, we have evaluated the oligomerization equilibrium for this protein fragment. Also, we have determined changes in the tertiary structure and its stability in a broad range of pH values by means of different spectroscopic methods. Additionally, we compared this fragment with the one that lacks the NLS employing experimental and computational methods. Finally, we evaluated the motion of dimeric forms to get insights into the conformational flexibility of this TDP-43 module in an oligomeric state. Our results suggest that this domain has a conformational plasticity in the vicinity of the single tryptophan of this domain (Trp68), which is enhanced by the presence of the nuclear localization signal. All these results help to understand the molecular features of the NTD of TDP-43.

Intracellular Conformation of Amyotrophic Lateral Sclerosis-Causative TDP-43

Transactive response element DNA/RNA-binding protein 43 kDa (TDP-43) is the causative protein of amyotrophic lateral sclerosis (ALS); several ALS-associated mutants of TDP-43 have been identified. TDP-43 has several domains: an N-terminal domain, two RNA/DNA-recognition motifs, and a C-terminal intrinsically disordered region (IDR). Its structures have been partially determined, but the whole structure remains elusive. In this study, we investigate the possible end-to-end distance between the N- and C-termini of TDP-43, its alterations due to ALS-associated mutations in the IDR, and its apparent molecular shape in live cells using Förster resonance energy transfer (FRET) and fluorescence correlation spectroscopy (FCS). Furthermore, the interaction between ALS-associated TDP-43 and heteronuclear ribonucleoprotein A1 (hnRNP A1) is slightly stronger than that of wild-type TDP-43. Our findings provide insights into the structure of wild-type and ALS-associated mutants of TDP-43 in a cell.

Cytoplasmic TDP-43 accumulation drives changes in C-bouton number and size in a mouse model of sporadic Amyotrophic Lateral Sclerosis

An altered neuronal excitability of spinal motoneurones has consistently been implicated in Amyotrophic Lateral Sclerosis (ALS) leading to several investigations of synaptic input to these motoneurones. One such input that has repeatedly been shown to be affected is a population of large cholinergic synapses terminating mainly on the soma of the motoneurones referred to as C-boutons. Most research on these synapses during disease progression has used transgenic Superoxide Dismutase 1 (SOD1) mouse models of the disease which have not only produced conflicting findings, but also fail to recapitulate the key pathological feature seen in ALS; cytoplasmic accumulations of TAR DNA-binding protein 43 (TDP-43). Additionally, they fail to distinguish between slow and fast motoneurones, the latter of which have more C-boutons, but are lost earlier in the disease. To circumvent these issues, we quantified the frequency and volume of C-boutons on traced soleus and gastrocnemius motoneurones, representing predominantly slow and fast motor pools respectively. Experiments were performed using the TDP-43ΔNLS mouse model that carries a transgenic construct of TDP-43 devoid of its nuclear localization signal, preventing its nuclear import. This results in the emergence of pathological TDP-43 inclusions in the cytoplasm, modelling the main pathology seen in this disorder, accompanied by a severe and lethal ALS phenotype. Our results confirmed changes in both the number and volume of C-boutons with a decrease in number on the more vulnerable, predominantly fast gastrocnemius motoneurones and an increase in number on the less vulnerable, predominantly slow soleus motoneurones. Importantly, these changes were only found in male mice. However, both sexes and motor pools showed a decrease in C-bouton volume. Our experiments confirm that cytoplasmic TDP-43 accumulation is sufficient to drive C-bouton changes.

Mechanisms underlying TDP-43 pathology and neurodegeneration: An updated Mini-Review

TAR DNA binding protein 43 kDa (TDP-43) plays an important role in several essential cell functions. However, TDP-43 dysfunction has been implicated in the development of various brain diseases including amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), and limbic predominant age-related TDP-43 encephalopathy (LATE). Recent investigations into the individual components of TDP-43 pathology show how broader TDP-43 dysfunction may precede these disease end states, and therefore could help to explain why TDP-43 dysfunction continues to be implicated in a rapidly expanding category of neurodegenerative diseases. The literature reviewed in this article suggests that dysregulation of TDP-43 initiated by some environmental and/or genetic insults can lead to a snowballing dysfunction across the cell, involving impaired gene expression, mRNA stability, as well as the function and coordination of those pathways directly regulated by TDP-43. Furthermore, the hallmarks of TDP-43 pathology, such as hyperphosphorylation and insoluble cytoplasmic accumulation of the protein may actually be artifacts of an upstream impairment in TDP-43's normal function. Overall, the present article summarizes current knowledge regarding TDP-43's normal and pathological cell functions and sheds light on possible mechanisms that underlie its causal role in neurodegeneration.

ALS-Linked A315T and A315E Mutations Enhance β-Barrel Formation of the TDP-43307-319 Hexamer: A REST2 Simulation Study

Pathogenic mutations of transactivation response element DNA-binding protein 43 (TDP-43) are closely linked with amyotrophic lateral sclerosis (ALS). It was recently reported that two ALS-linked familial mutants A315T and A315E of TDP-43_307-319 peptides can self-assemble into oligomers including tetramers, hexamers, and octamers, among which hexamers were suggested to form the β-barrel structure. However, due to the transient nature of oligomers, their conformational properties and the atomic mechanisms underlying the β-barrel formation remain largely elusive. Herein, we investigated the hexameric conformational distributions of the wild-type (WT) TDP-43_307-319 fragment and its A315T and A315E mutants by performing all-atom explicit-solvent replica exchange with solute tempering 2 simulations. Our simulations reveal that each peptide can self-assemble into diverse conformations including ordered β-barrels, bilayer β-sheets and/or monolayer β-sheets, and disordered complexes. A315T and A315E mutants display higher propensity to form β-barrel structures than the WT, which provides atomic explanation for their enhanced neurotoxicity reported previously. Detailed interaction analysis shows that A315T and A315E mutations increase inter-molecular interactions. Also, the β-barrel structures formed by the three different peptides are stabilized by distinct inter-peptide side-chain hydrogen bonding, hydrophobic, and aromatic stacking interactions. This study demonstrates the enhanced β-barrel formation of the TDP-43_307-319 hexamer by the pathogenic A315T and A315E mutations and reveals the underlying molecular determinants, which may be helpful for in-depth understanding of the ALS-mutation-induced neurotoxicity of TDP-43 protein.

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.

MicroRNA-183-5p regulates TAR DNA-binding protein 43 neurotoxicity via SQSTM1/p62 in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that selectively attacks motor neurons, and leads to progressive muscle weakness and death. A common pathological feature is the misfolding, aggregation, and cytoplasmic mislocalization of TAR DNA-binding protein 43 (TDP-43) proteins in more than 95% of ALS patients, suggesting a universal role TDP-43 proteinopathy in ALS. Mutations in SQSTM1/p62 have been identified in familial and sporadic cases of ALS. MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate their target genes. Emerging evidence indicates that miRNA dysregulation is associated with neuronal toxicity and mitochondrial dysfunction, and also plays a pivotal role in ALS pathogenesis. Here, we report the first evidence that miR-183-5p is aberrantly upregulated in spinal cords of patients with ALS. Using luciferase reporter assays and miR-183-5p agomirs, we demonstrate that miR-183-5p regulates the SQSTM1/p62 3'-untranslated region to suppress expression. A miR-183-5p agomir attenuated SOSTM1/p62 expression and led to an increase in TDP-43 protein levels in neuronal and non-neuronal cells. In contrast, a miR-183-5p antagomir decreased TDP-43 but increased SQSTM1/p62 protein levels. The antagomir repressed formation of stress granules and aggregated TDP43 protein in neuronal cells under stress-induced conditions and protected against cytotoxicity. Knockdown of SQSTM1/p62 decreased total ubiquitination and increased TDP-43 protein aggregation, indicating that SQSTM1/p62 may play a protective role in cells. In summary, our study reveals a novel mechanism of TDP-43 proteinopathy mediated by the miR-183-5p and provides a molecular link between aberrant RNA processing and protein degradation, two major pillars in ALS pathogenesis.

The unique neuropathological vulnerability of the human brain to aging

Alzheimer's disease (AD)-related neurofibrillary tangles (NFT), argyrophilic grain disease (AGD), aging-related tau astrogliopathy (ARTAG), limbic predominant TDP-43 proteinopathy (LATE), and amygdala-predominant Lewy body disease (LBD) are proteinopathies that, together with hippocampal sclerosis, progressively appear in the elderly affecting from 50% to 99% of individuals aged 80 years, depending on the disease. These disorders usually converge on the same subject and associate with additive cognitive impairment. Abnormal Tau, TDP-43, and α-synuclein pathologies progress following a pattern consistent with an active cell-to-cell transmission and abnormal protein processing in the host cell. However, cell vulnerability and transmission pathways are specific for each disorder, albeit abnormal proteins may co-localize in particular neurons. All these alterations are unique or highly prevalent in humans. They all affect, at first, the archicortex and paleocortex to extend at later stages to the neocortex and other regions of the telencephalon. These observations show that the phylogenetically oldest areas of the human cerebral cortex and amygdala are not designed to cope with the lifespan of actual humans. New strategies aimed at reducing the functional overload of the human telencephalon, including optimization of dream repair mechanisms and implementation of artificial circuit devices to surrogate specific brain functions, appear promising.

Intrathecal Pseudodelivery of Drugs in the Therapy of Neurodegenerative Diseases: Rationale, Basis and Potential Applications

Intrathecal pseudodelivery of drugs is a novel route to administer medications to treat neurodegenerative diseases based on the CSF-sink therapeutic strategy by means of implantable devices. While the development of this therapy is still in the preclinical stage, it offers promising advantages over traditional routes of drug delivery. In this paper, we describe the rationale of this system and provide a technical report on the mechanism of action, that relies on the use of nanoporous membranes enabling selective molecular permeability. On one side, the membranes do not permit the crossing of certain drugs; whereas, on the other side, they permit the crossing of target molecules present in the CSF. Target molecules, by binding drugs inside the system, are retained or cleaved and subsequently eliminated from the central nervous system. Finally, we provide a list of potential indications, the respective molecular targets, and the proposed therapeutic agents.

Mixed pathology as a rule, not exception: Time to reconsider disease nosology

Parkinson's disease is a progressive neurodegenerative disorder that is associated with motor and nonmotor symptoms. Accumulation of misfolded α-synuclein is considered a key pathological feature during disease initiation and progression. While clearly deemed a synucleinopathy, the development of amyloid-β plaques, tau-containing neurofibrillary tangles, and even TDP-43 protein inclusions occur within the nigrostriatal system and in other brain regions. In addition, inflammatory responses, manifested by glial reactivity, T-cell infiltration, and increased expression of inflammatory cytokines, plus other toxic mediators derived from activated glial cells, are currently recognized as prominent drivers of Parkinson's disease pathology. However, copathologies have increasingly been recognized as the rule (>90%) and not the exception, with Parkinson's disease cases on average exhibiting three different copathologies. While microinfarcts, atherosclerosis, arteriolosclerosis, and cerebral amyloid angiopathy may have an impact on disease progression, α-synuclein, amyloid-β, and TDP-43 pathology do not seem to contribute to progression.

Biomarkers: Role and Scope in Neurological Disorders

Neurological disorders pose a great threat to social health and are a major cause for mortality and morbidity. Effective drug development complemented with the improved drug therapy has made considerable progress towards easing symptoms associated with neurological illnesses, yet poor diagnosis and imprecise understanding of these disorders has led to imperfect treatment options. The scenario is complicated by the inability to extrapolate results of cell culture studies and transgenic models to clinical applications which has stagnated the process of improving drug therapy. In this context, the development of biomarkers has been viewed as beneficial to easing various pathological complications. A biomarker is measured and evaluated in order to gauge the physiological process or a pathological progression of a disease and such a marker can also indicate the clinical or pharmacological response to a therapeutic intervention. The development and identification of biomarkers for neurological disorders involves several issues including the complexity of the brain, unresolved discrepant data from experimental and clinical studies, poor clinical diagnostics, lack of functional endpoints, and high cost and complexity of techniques yet research in the area of biomarkers is highly desired. The present work describes existing biomarkers for various neurological disorders, provides support for the idea that biomarker development may ease our understanding underlying pathophysiology of these disorders and help to design and explore therapeutic targets for effective intervention.

Molecular mechanisms of amyotrophic lateral sclerosis as broad therapeutic targets for gene therapy applications utilizing adeno-associated viral vectors

Despite the devastating clinical outcome of the neurodegenerative disease, amyotrophic lateral sclerosis (ALS), its etiology remains mysterious. Approximately 90% of ALS is characterized as sporadic, signifying that the patient has no family history of the disease. The development of an impactful disease modifying therapy across the ALS spectrum has remained out of grasp, largely due to the poorly understood mechanisms of disease onset and progression. Currently, ALS is invariably fatal and rapidly progressive. It is hypothesized that multiple factors can lead to the development of ALS, however, treatments are often focused on targeting specific familial forms of the disease (10% of total cases). There is a strong need to develop disease modifying treatments for ALS that can be effective across the full ALS spectrum of familial and sporadic cases. Although the onset of disease varies significantly between patients, there are general disease mechanisms and progressions that can be seen broadly across ALS patients. Therefore, this review explores the targeting of these widespread disease mechanisms as possible areas for therapeutic intervention to treat ALS broadly. In particular, this review will focus on targeting mechanisms of defective protein homeostasis and RNA processing, which are both increasingly recognized as design principles of ALS pathogenesis. Additionally, this review will explore the benefits of gene therapy as an approach to treating ALS, specifically focusing on the use of adeno-associated virus (AAV) as a vector for gene delivery to the CNS and recent advances in the field.

Role of Triggers on the Structural and Functional Facets of TAR DNA-binding Protein 43

Nuclear TAR DNA-binding protein 43 (TDP-43) mitigates cellular function, but the dynamic nucleus-cytoplasm shuttling of TDP-43 is disrupted in diseases, such as Amyotrophic Lateral Sclerosis (ALS). The polymorphic nature of the TDP-43 structures in vitro and in vivo is a result of environmental factors leading to the protein pathogenesis. Once the triggers which mitigate TDP-43 biochemistry are identified, new therapies can be developed. This review aims to illustrate recent discoveries in the diversity of TDP-43 structures (amyloidogenic and non-amyloidogenic) and highlight the triggers which result in their formation.

PINK1/Parkin-mediated mitophagy in neurodegenerative diseases

Mitochondria play key roles in bioenergetics, metabolism, and signaling; therefore, stable mitochondrial function is essential for cell survival, particularly in energy-intensive neuronal cells. In neurodegenerative diseases, damaged mitochondria accumulate in neurons causing associated bioenergetics deficiency, impaired cell signaling, defective cytoplasmic calcium buffering, and other pathological changes. Mitochondrial quality control is an important mechanism to ensure the maintenance of mitochondrial health, homeostasis, and mitophagy, the latter of which is a pathway that delivers defective mitochondria to the lysosome for degradation. Defective mitophagy is thought to be responsible for the accumulation of damaged mitochondria, which leads to cellular dysfunction and/or death in neurodegenerative diseases. PINK1/Parkin mainly regulates ubiquitin-dependent mitophagy, which is crucial for many aspects of mitochondrial physiology, particularly the initiation of autophagic mechanisms. Therefore, in the present review, we summarize the current knowledge of the conventional mitophagy pathway, focusing on the molecular mechanisms underlying mitophagy dysregulation in prion disease and other age-related neurodegenerative diseases, especially in relation to the PINK1/Parkin pathway. Moreover, we list the inducers of mitophagy that possess neuroprotective effects, in addition to their mechanisms related to the PINK1/Parkin pathway. These mechanisms may provide potential interventions centered on the regulation of mitophagy and offer therapeutic strategies for the treatment of neurodegenerative diseases.

Sequence determinants and solution conditions underlying liquid to solid phase transition

Life consists of numberless functional biomolecules that exist in various states. Besides well-dissolved phases, biomolecules especially proteins and nucleic acids can form liquid droplets through liquid-liquid phase separation (LLPS). Stronger interactions promote a solid-like state of biomolecular condensates, which are also formerly referred to as detergent-insoluble aggregates. Solid-like condensates exist in vivo physiologically and pathologically, and their formation has not been fully understood. Recently, more and more research has proven that liquid to solid phase transition (LST) is an essential way to form solid condensates. In this review, we summarized the regions in the sequence that have different impacts on phase transition and emphasized that the LST is affected by its sequence characteristics. Moreover, increasing evidence unveiled that LST is affected by various solution conditions. We discussed solution conditions like protein concentration, pH, ATP, ions, and small molecules in a solution. Methods have been established to study these solid phase components. Here, we summarized low-throughput experimental techniques and high-throughput omics methods in the study of the LST.

Loss of TDP-43 function underlies hippocampal and cortical synaptic deficits in TDP-43 proteinopathies

TDP-43 proteinopathy is linked to neurodegenerative diseases that feature synaptic loss in the cortex and hippocampus, although it remains unclear how TDP-43 regulates mature synapses. We report that, in adult mouse hippocampus, TDP-43 knockdown, but not overexpression, induces robust structural and functional damage to excitatory synapses, supporting a role for TDP-43 in maintaining mature synapses. Dendritic spine loss induced by TDP-43 knockdown is rescued by wild-type TDP-43, but not ALS/FTLD-associated mutants, suggesting a common TDP-43 functional deficiency in neurodegenerative diseases. Interestingly, M337V and A90V mutants also display dominant negative activities against WT TDP-43, partially explaining why M337V transgenic mice develop hippocampal degeneration similar to that in excitatory neuronal TDP-43 knockout mice, and why A90V mutation is associated with Alzheimer's disease. Further analyses reveal that a TDP-43 knockdown-induced reduction in GluN2A contributes to synaptic loss. Our results show that loss of TDP-43 function underlies hippocampal and cortical synaptic degeneration in TDP-43 proteinopathies.

Vascular and Nonvascular Mechanisms of Cognitive Impairment and Dementia

Aging, familial gene mutations, and genetic, environmental, and modifiable lifestyle risk factors predispose individuals to cognitive impairment or dementia by influencing the efficacy of multiple, often interdependent cellular and molecular homeostatic pathways mediating neuronal, glial, and vascular integrity and, ultimately, cognitive status. This review summarizes data from foundational and recent breakthrough studies to highlight common and differential vascular and nonvascular pathogenic mechanisms underlying the progression of Alzheimer disease, vascular dementia, frontotemporal dementia, and dementia with Lewy bodies.

Modular architecture and functional annotation of human RNA-binding proteins containing RNA recognition motif

RNA-binding proteins (RBPs) are structurally and functionally diverse macromolecules with significant involvement in several post-transcriptional gene regulatory processes and human diseases. RNA recognition motif (RRM) is one of the most abundant RNA-binding domains in human RBPs. The unique modular architecture of each RBP containing RRM is crucial for its diverse target recognition and function. Genome-wide study of these structurally conserved and functionally diverse domains can enhance our understanding of their functional implications. In this study, modular architecture of RRM containing RBPs in human proteome is identified and systematically analysed. We observe that 30% of human RBPs with RNA-binding function contain RRM in single or multiple repeats or with other domains with maximum of six repeats. Zinc-fingers are the most frequently co-occurring domain partner of RRMs. Human RRM containing RBPs mostly belong to RNA metabolism class of proteins and are significantly enriched in two functional pathways including spliceosome and mRNA surveillance. Various human diseases are associated with 18% of the RRM containing RBPs. Single RRM containing RBPs are highly enriched in disorder regions. Gene ontology (GO) molecular functions including poly(A), poly(U) and miRNA binding are highly depleted in RBPs with single RRM, indicating the significance of modular nature of RRMs in specific function. The current study reports all the possible domain architectures of RRM containing human RBPs and their functional enrichment. The idea of domain architecture, and how they confer specificity and new functionalities to RBPs, can help in re-designing of modular RRM containing RBPs with re-engineered function.

The Role of TAR DNA Binding Protein 43 (TDP-43) as a CandiDate Biomarker of Amyotrophic Lateral Sclerosis: A Systematic Review and Meta-Analysis

BACKGROUND

TAR DNA-binding protein 43 (TDP-43) aggregation in neuronal cells is recognized as a hallmark of amyotrophic lateral sclerosis (ALS). Although the literature strongly supports the pathogenetic role of TDP-43 in ALS pathogenesis, the role of TDP-43 as a biomarker of ALS is controversial. We performed a systematic review and meta-analysis to assess the diagnostic performance of TDP-43 for ALS.

METHODS

Relevant publications were identified by a systematic literature search on PubMed and Web of Science from their inception to 8 April 2022.

RESULTS

Seven studies, including 472 individuals, of whom 254 had ALS according to the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale, met the inclusion criteria for our meta-analysis. According to the random-effects model, CSF TDP-43 levels are higher in ALS patients compared with control groups.

CONCLUSIONS

CSF TDP-43 could represent a biomarker of ALS, but further studies are mandatory before drawing conclusions.

Involvement of heterologous ubiquitination including linear ubiquitination in Alzheimer's disease and amyotrophic lateral sclerosis

In neurodegenerative diseases such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), the progressive accumulation of ubiquitin-positive cytoplasmic inclusions leads to proteinopathy and neurodegeneration. Along with the seven types of Lys-linked ubiquitin chains, the linear ubiquitin chain assembly complex (LUBAC)-mediated Met1-linked linear ubiquitin chain, which activates the canonical NF-κB pathway, is also involved in cytoplasmic inclusions of tau in AD and TAR DNA-binding protein 43 in ALS. Post-translational modifications, including heterologous ubiquitination, affect proteasomal and autophagic degradation, inflammatory responses, and neurodegeneration. Single nucleotide polymorphisms (SNPs) in SHARPIN and RBCK1 (which encodes HOIL-1L), components of LUBAC, were recently identified as genetic risk factors of AD. A structural biological simulation suggested that most of the SHARPIN SNPs that cause an amino acid replacement affect the structure and function of SHARPIN. Thus, the aberrant LUBAC activity is related to AD. Protein ubiquitination and ubiquitin-binding proteins, such as ubiquilin 2 and NEMO, facilitate liquid-liquid phase separation (LLPS), and linear ubiquitination seems to promote efficient LLPS. Therefore, the development of therapeutic approaches that target ubiquitination, such as proteolysis-targeting chimeras (PROTACs) and inhibitors of ubiquitin ligases, including LUBAC, is expected to be an additional effective strategy to treat neurodegenerative diseases.

Personalized Precision Immunotherapy for Amyotrophic Lateral Sclerosis (ALS)

Neurological syndrome amyotrophic lateral sclerosis (ALS) affects motor neurons and is characterized by progressive motor neuron loss in the brain and spinal cord. ALS starts with mainly focal onset but when the disease progresses, it spreads to different parts of the body, with survival limits of 2-5 years after disease initiation. To date, only supportive care is provided for ALS patients, and no effective treatment or cure has been discovered. This review is focused on clinical and immunological aspects of ALS patients, based on our case studies, and we discuss the treatment we have provided to those patients based on a detailed evaluation of their peripheral blood immune cells and blood-derived serum secreted factors, cytokines, chemokines and growth factors. We show that using a personalized approach of low dose immunotherapy there is an improvement in the effects on inflammation and immunological dysfunction.

Prospects for gene replacement therapies in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating and incurable neurodegenerative disease characterized by the progressive loss of upper and lower motor neurons. ALS causes death, usually within 2-5 years of diagnosis. Riluzole, the only drug currently approved in Europe for the treatment of this condition, offers only a modest benefit, increasing survival by 3 months on average. Recent advances in our understanding of causative or disease-modifying genetic variants and in the development of genetic therapy strategies present exciting new therapeutic opportunities for ALS. In addition, the approval of adeno-associated virus-mediated delivery of functional copies of the SMN1 gene to treat spinal muscular atrophy represents an important therapeutic milestone and demonstrates the potential of gene replacement therapies for motor neuron disorders. In this Review, we describe the current landscape of genetic therapies in ALS, highlighting achievements and critical challenges. In particular, we discuss opportunities for gene replacement therapy in subgroups of people with ALS, and we describe loss-of-function mutations that are known to contribute to the pathophysiology of ALS and could represent novel targets for gene replacement therapies.

Novel therapeutic approaches for motor neuron disease

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that leads to the neurodegeneration and death of upper and lower motor neurons (MNs). Although MNs are the main cells involved in the process of neurodegeneration, a growing body of evidence points toward other cell types as concurrent to disease initiation and propagation. Given the current absence of effective therapies, the quest for other therapeutic targets remains open and still challenges the scientific community. Both neuronal and extra-neuronal mechanisms of cellular stress and damage have been studied and have posed the basis for the development of novel therapies that have been investigated on both animal models and humans. In this chapter, a thorough review of the main mechanisms of cellular damage and the respective therapeutic attempts targeting them is reported. The main areas covered include neuroinflammation, protein aggregation, RNA metabolism, and oxidative stress.

Boosting Mitochondrial Potential: An Imperative Therapeutic Intervention in Amyotrophic Lateral Sclerosis

BACKGROUND

Amyotrophic Lateral Sclerosis (ALS) is a progressive and terminal neurodegenerative disorder. Mitochondrial dysfunction, imbalance of cellular bioenergetics, electron chain transportation and calcium homeostasis are deeply associated with the progression of this disease. Impaired mitochondrial functions are crucial in rapid neurodegeneration. The mitochondria of ALS patients are associated with deregulated Ca2+ homeostasis and elevated levels of reactive oxygen species (ROS), leading to oxidative stress. Overload of mitochondrial calcium and ROS production leads to glutamatereceptor mediated neurotoxicity. This implies mitochondria are an attractive therapeutic target.

OBJECTIVE

The aim of this review is to brief the latest developments in the understanding of mitochondrial pathogenesis in ALS and emphasize the restorative capacity of therapeutic candidates.

RESULTS

In ALS, mitochondrial dysfunction is a well-known phenomenon. Various therapies targeted towards mitochondrial dysfunction aim at decreasing ROS generation, increasing mitochondrial biogenesis, and inhibiting apoptotic pathways. Some of the therapies briefed in this review may be categorized as synthetic, natural compounds, genetic materials, and cellular therapies.

CONCLUSION

The overarching goals of mitochondrial therapies in ALS are to benefit ALS patients by slowing down the disease progression and prolonging overall survival. Despite various therapeutic approaches, there are many hurdles in the development of a successful therapy due to the multifaceted nature of mitochondrial dysfunction and ALS progression. Intensive research is required to precisely elucidate the molecular pathways involved in the progression of mitochondrial dysfunctions that ultimately lead to ALS. Because of the multifactorial nature of ALS, a combination therapy approach may hold the key to cure and treat ALS in the future.

Amyotrophic Lateral Sclerosis Risk Genes and Suppressor

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that leads to death by progressive paralysis and respiratory failure within 2-4 years of onset. About 90-95% of ALS cases are sporadic (sALS), and 5-10% are inherited through family (fALS). Though the mechanisms of the disease are still poorly understood, so far, approximately 40 genes have been reported as ALS causative genes. The mutations in some crucial genes, like SOD1, C9ORF72, FUS, and TDP-43, are majorly associated with ALS, resulting in ROS-associated oxidative stress, excitotoxicity, protein aggregation, altered RNA processing, axonal and vesicular trafficking dysregulation, and mitochondrial dysfunction. Recent studies show that dysfunctional cellular pathways get restored as a result of the repair of a single pathway in ALS. In this review article, our aim is to identify putative targets for therapeutic development and the importance of a single suppressor to reduce multiple symptoms by focusing on important mutations and the phenotypic suppressors of dysfunctional cellular pathways in crucial genes as reported by other studies.

Inflammation-Mediated Responses in the Development of Neurodegenerative Diseases

Since its first description over a century ago, neurodegenerative diseases (NDDs) have impaired the lives of millions of people worldwide. As one of the major threats to human health, NDDs are characterized by progressive loss of neuronal structure and function, leading to the impaired function of the CNS. While the precise mechanisms underlying the emergence of NDDs remains elusive, association of neuroinflammation with the emergence of NDDs has been suggested. The immune system is tightly controlled to maintain homeostatic milieu and failure in doing so has been shown catastrophic. Here, we review current concepts on the cellular and molecular drivers responsible in the induction of neuroinflammation and how such event further promotes neuronal damage leading to neurodegeneration. Experimental data generated from cell culture and animal studies, gross and molecular pathologies of human CNS samples, and genome-wide association study are discussed to provide deeper insights into the mechanistic details of neuroinflammation and its roles in the emergence of NDDs.

Factors affecting do-not-resuscitate decisions among patients with amyotrophic lateral sclerosis in Taiwan

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease. Usually, patients survive for approximately 2-4 years after the onset of the disease, and they often die of respiratory failure. This study examined the factors associated with signing a "do not resuscitate" (DNR) form in patients with ALS. This cross-sectional study included patients diagnosed with ALS between January 2015 and December 2019 in a Taipei City hospital. We recorded patients' age at disease onset; sex; presence of diabetes mellitus, hypertension, cancer, or depression; use of invasive positive pressure ventilator (IPPV) or non-IPPV (NIPPV); use of nasogastric tube (NG) or percutaneous endoscopic gastrostomy (PEG) tube; follow-up years; and number of hospitalizations. Data from 162 patients were recorded (99 men). Fifty-six (34.6%) signed a DNR. Multivariate logistic regression analyses revealed that the factors associated with DNR included NIPPV (OR = 6.95, 95% CI = 2.21-21.84), PEG tube feeding (OR = 2.86, 95% CI = 1.13-7.24), NG tube feeding (OR = 5.75, 95% CI = 1.77-18.65), follow-up years (OR = 1.13, 95% CI = 1.02-1.26), and number of hospital admissions (OR = 1.26, 95% CI = 1.02-1.57). The findings suggest that end-of-life decision making among patients with ALS may often be delayed. DNR decisions should be discussed with patients and their families during the early stages of disease progression. Physicians are advised to discuss DNR with patients when they can speak and to offer palliative care options.

Role of piRNA biogenesis and its neuronal function in the development of neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), are caused by neuronal loss and dysfunction. Despite remarkable improvements in our understanding of these pathogeneses, serious worldwide problems with significant public health burdens are remained. Therefore, new efficient diagnostic and therapeutic strategies are urgently required. PIWI-interacting RNAs (piRNAs) are a major class of small non-coding RNAs that silence gene expression through transcriptional and post-transcriptional processes. Recent studies have demonstrated that piRNAs, originally found in the germ line, are also produced in non-gonadal somatic cells, including neurons, and further revealed the emerging roles of piRNAs, including their roles in neurodevelopment, aging, and neurodegenerative diseases. In this review, we aimed to summarize the current knowledge regarding the piRNA roles in the pathophysiology of neurodegenerative diseases. In this context, we first reviewed on recent updates on neuronal piRNA functions, including biogenesis, axon regeneration, behavior, and memory formation, in humans and mice. We also discuss the aberrant expression and dysregulation of neuronal piRNAs in neurodegenerative diseases, such as AD, PD, and ALS. Moreover, we review pioneering preclinical studies on piRNAs as biomarkers and therapeutic targets. Elucidation of the mechanisms underlying piRNA biogenesis and their functions in the brain would provide new perspectives for the clinical diagnosis and treatment of AD and various neurodegenerative diseases.

Co-administration of Nanowired DL-3-n-Butylphthalide (DL-NBP) Together with Mesenchymal Stem Cells, Monoclonal Antibodies to Alpha Synuclein and TDP-43 (TAR DNA-Binding Protein 43) Enhance Superior Neuroprotection in Parkinson's Disease Following Concussive Head Injury

dl-3-n-butylphthalide (dl-NBP) is one of the potent antioxidant compounds that induces profound neuroprotection in stroke and traumatic brain injury. Our previous studies show that dl-NBP reduces brain pathology in Parkinson's disease (PD) following its nanowired delivery together with mesenchymal stem cells (MSCs) exacerbated by concussive head injury (CHI). CHI alone elevates alpha synuclein (ASNC) in brain or cerebrospinal fluid (CSF) associated with elevated TAR DNA-binding protein 43 (TDP-43). TDP-43 protein is also responsible for the pathologies of PD. Thus, it is likely that exacerbation of brain pathology in PD following brain injury may be thwarted using nanowired delivery of monoclonal antibodies (mAb) to ASNC and/or TDP-43. In this review, the co-administration of dl-NBP with MSCs and mAb to ASNC and/or TDP-43 using nanowired delivery in PD and CHI-induced brain pathology is discussed based on our own investigations. Our observations show that co-administration of TiO2 nanowired dl-NBP with MSCs and mAb to ASNC with TDP-43 induced superior neuroprotection in CHI induced exacerbation of brain pathology in PD, not reported earlier.

Interlinked role of ASN, TDP-43 and Miro1 with parkinopathy: Focus on targeted approach against neuropathy in parkinsonism

Parkinsonism is a complex neurodegenerative disease that is difficult to differentiate because of its idiopathic and unknown origins. The hereditary parkinsonism known as autosomal recessive-juvenile parkinsonism (AR-JP) is marked by tremors, dyskinesias, dystonic characteristics, and manifestations that improve sleep but do not include dementia. This was caused by deletions and point mutations in PARK2 (chromosome 6q25.2-27). Diminished or unusual sensations (paresthesias), loss of neuron strength both in the CNS and peripheral nerves, and lack of motor coordination are the hallmarks of neuropathy in parkinsonism. The incidence of parkinsonism during oxidative stress and ageing is associated with parkinopathy. Parkinopathy is hypothesized to be triggered by mutation of the parkin (PRKN) gene and loss of normal physiological functions of PRKN proteins, which triggers their pathogenic aggregation due to conformational changes. Two important genes that control mitochondrial health are PRKN and phosphatase and tensin homologue deleted on chromosome 10-induced putative kinase 1 (PINK1). Overexpression of TAR DNA-binding protein-43 (TDP-43) increases the aggregation of insoluble PRKN proteins in OMM. Foreign α-synuclein (ASN) promotes parkinopathy via S-nitrosylation and hence has a neurotoxic effect on dopaminergic nerves. Miro1 (Miro GTPase1), a member of the RAS superfamily, is expressed in nerve cells. Due to PINK1/PRKN and Miro1's functional relationship, an excess of mitochondrial calcium culminates in the destruction of dopaminergic neurons. An interlinked understanding of TDP-43, PINK1/PRKN, ASN, and Miro1 signalling in the communication among astrocytes, microglia, neurons, and immune cells within the brain explored the pathway of neuronal death and shed light on novel strategies for the diagnosis and treatment of parkinsonism.

Multistep molecular mechanism of amyloid-like aggregation of nucleic acid-binding domain of TDP-43

TDP-43 protein is associated with many neurodegenerative diseases and has been shown to adopt various oligomeric and fibrillar states. However, a detailed kinetic understanding of the structural transformation of the native form of the protein to the fibrillar state is missing. In this study, we delineate the temporal sequence of structural events during the amyloid-like assembly of the functional nucleic acid-binding domain of TDP-43. We kinetically mapped the aggregation process using multiple probes such as tryptophan and thioflavin T (ThT) fluorescence, circular dichroism (CD), and dynamic light scattering (DLS) targeting different structural events. Our data reveal that aggregation occurs in four distinct steps-very fast, fast, slow, and very slow. The "very fast" change results in partially unfolded forms that undergo conformational conversion, oligomerization and bind to ThT in the "fast step" to form higher order intermediates (HOI). The temporal sequence of the formation of ThT binding sites and conformational conversion depends upon the protein concentration. The HOI further undergoes structural rearrangement to form protofibrils in the "slow" step, which, consequently, assembles in the "very slow" step to form an amyloid-like assembly. The spectroscopic properties of the amyloid-like assembly across the protein concentration remain similar. Additionally, we observe no lag phase across protein concentration for all the probes studied, suggesting that the aggregation process follows a linear polymerization reaction. Overall, our study demonstrates that the amyloid-like assembly forms in multiple steps, which is also supported by the temperature dependence of the kinetics.

Dysregulated Expression of Transposable Elements in TDP-43M337V Human Motor Neurons That Recapitulate Amyotrophic Lateral Sclerosis In Vitro

Amyotrophic lateral sclerosis (ALS) is a disease that progressively annihilates spinal cord motor neurons, causing severe motor decline and death. The disease is divided into familial and sporadic ALS. Mutations in the TAR DNA binding protein 43 (TDP-43) have been involved in the pathological emergence and progression of ALS, although the molecular mechanisms eliciting the disease are unknown. Transposable elements (TEs) and DNA sequences capable of transposing within the genome become dysregulated and transcribed in the presence of TDP-43 mutations. We performed RNA-Seq in human motor neurons (iMNs) derived from induced pluripotent stem cells (iPSCs) from TDP-43 wild-type-iMNs-TDP-43^WT-and mutant-iMNs-TDP-43^M337V-genotypes at 7 and 14 DIV, and, with state-of-the-art bioinformatic tools, analyzed whether TDP-43^M337V alters both gene expression and TE activity. Our results show that TDP-43^M337V induced global changes in the gene expression and TEs levels at all in vitro stages studied. Interestingly, many genetic pathways overlapped with that of the TEs activity, suggesting that TEs control the expression of several genes. TEs correlated with genes that played key roles in the extracellular matrix and RNA processing: all the regulatory pathways affected in ALS. Thus, the loss of TE regulation is present in TDP-43 mutations and is a critical determinant of the disease in human motor neurons. Overall, our results support the evidence that indicates TEs are critical regulatory sequences contributing to ALS neurodegeneration.

Corrigendum: TDP-43 and NEAT long non-coding RNA: Roles in neurodegenerative disease

[This corrects the article DOI: 10.3389/fncel.2022.954912.].

Allele-specific silencing as therapy for familial amyotrophic lateral sclerosis caused by the p.G376D TARDBP mutation

Amyotrophic lateral sclerosis is a neurodegenerative disease characterized by the degeneration of motor neurons. There is no treatment for this disease that affects the ability to move, eat, speak and finally breathe, causing death. In an Italian family, a heterozygous pathogenic missense variant has been previously discovered in Exon 6 of the gene TARDBP encoding the TAR DNA-binding protein 43 protein. Here, we developed a potential therapeutic tool based on allele-specific small interfering RNAs for familial amyotrophic lateral sclerosis with the heterozygous missense mutation c.1127G>A. We designed a small interfering RNA that was able to diminish specifically the expression of the exogenous Green Fluorescent Protein (TAR DNA-binding protein 43^G376D mutant protein) in HEK-293T cells but not that of the Green Fluorescent Protein (TAR DNA-binding protein 43 wild-type). Similarly, this small interfering RNA silenced the mutated allele in fibroblasts derived from patients with amyotrophic lateral sclerosis but did not silence the wild-type gene in control fibroblasts. In addition, we established that silencing the mutated allele was able to strongly reduce the pathological cellular phenotypes induced by TAR DNA-binding protein 43^G376D expression, such as the presence of cytoplasmic aggregates. Thus, we have identified a small interfering RNA that could be used to silence specifically the mutated allele to try a targeted therapy for patients carrying the p.G376D TAR DNA-binding protein 43 mutation.

Intrinsically disordered regions that drive phase separation form a robustly distinct protein class

Protein phase separation is thought to be a primary driving force for the formation of membrane-less organelles, which control a wide range of biological functions from stress response to ribosome biogenesis. Among phase-separating (PS) proteins, many have intrinsically disordered regions (IDRs) that are needed for phase separation to occur. Accurate identification of IDRs that drive phase separation is important for testing the underlying mechanisms of phase separation, identifying biological processes that rely on phase separation, and designing sequences that modulate phase separation. To identify IDRs that drive phase separation, we first curated datasets of folded, ID, and PS ID sequences. We then used these sequence sets to examine how broadly existing amino acid property scales can be used to distinguish between the three classes of protein regions. We found that there are robust property differences between the classes and, consequently, that numerous combinations of amino acid property scales can be used to make robust predictions of protein phase separation. This result indicates that multiple, redundant mechanisms contribute to the formation of phase-separated droplets from IDRs. The top-performing scales were used to further optimize our previously developed predictor of PS IDRs, ParSe. We then modified ParSe to account for interactions between amino acids and obtained reasonable predictive power for mutations that have been designed to test the role of amino acid interactions in driving protein phase separation. Collectively, our findings provide further insight into the classification of IDRs and the elements involved in protein phase separation.

Nuclear import receptors are recruited by FG-nucleoporins to rescue hallmarks of TDP-43 proteinopathy

BACKGROUND

Cytoplasmic mislocalization and aggregation of TAR DNA-binding protein-43 (TDP-43) is a hallmark of the amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD) disease spectrum, causing both nuclear loss-of-function and cytoplasmic toxic gain-of-function phenotypes. While TDP-43 proteinopathy has been associated with defects in nucleocytoplasmic transport, this process is still poorly understood. Here we study the role of karyopherin-β1 (KPNB1) and other nuclear import receptors in regulating TDP-43 pathology.

METHODS

We used immunostaining, immunoprecipitation, biochemical and toxicity assays in cell lines, primary neuron and organotypic mouse brain slice cultures, to determine the impact of KPNB1 on the solubility, localization, and toxicity of pathological TDP-43 constructs. Postmortem patient brain and spinal cord tissue was stained to assess KPNB1 colocalization with TDP-43 inclusions. Turbidity assays were employed to study the dissolution and prevention of aggregation of recombinant TDP-43 fibrils in vitro. Fly models of TDP-43 proteinopathy were used to determine the effect of KPNB1 on their neurodegenerative phenotype in vivo.

RESULTS

We discovered that several members of the nuclear import receptor protein family can reduce the formation of pathological TDP-43 aggregates. Using KPNB1 as a model, we found that its activity depends on the prion-like C-terminal region of TDP-43, which mediates the co-aggregation with phenylalanine and glycine-rich nucleoporins (FG-Nups) such as Nup62. KPNB1 is recruited into these co-aggregates where it acts as a molecular chaperone that reverses aberrant phase transition of Nup62 and TDP-43. These findings are supported by the discovery that Nup62 and KPNB1 are also sequestered into pathological TDP-43 aggregates in ALS/FTD postmortem CNS tissue, and by the identification of the fly ortholog of KPNB1 as a strong protective modifier in Drosophila models of TDP-43 proteinopathy. Our results show that KPNB1 can rescue all hallmarks of TDP-43 pathology, by restoring its solubility and nuclear localization, and reducing neurodegeneration in cellular and animal models of ALS/FTD.

CONCLUSION

Our findings suggest a novel NLS-independent mechanism where, analogous to its canonical role in dissolving the diffusion barrier formed by FG-Nups in the nuclear pore, KPNB1 is recruited into TDP-43/FG-Nup co-aggregates present in TDP-43 proteinopathies and therapeutically reverses their deleterious phase transition and mislocalization, mitigating neurodegeneration.

Mushroom Natural Products in Neurodegenerative Disease Drug Discovery

The variety of drugs available to treat neurodegenerative diseases is limited. Most of these drug's efficacy is restricted by individual genetics and disease stages and usually do not prevent neurodegeneration acting long after irreversible damage has already occurred. Thus, drugs targeting the molecular mechanisms underlying subsequent neurodegeneration have the potential to negate symptom manifestation and subsequent neurodegeneration. Neuroinflammation is a common feature of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis, and is associated with the activation of the NLRP3 inflammasome, which in turn leads to neurodegeneration. Inflammasome activation and oligomerisation is suggested to be a major driver of disease progression occurring in microglia. With several natural products and natural product derivatives currently in clinical trials, mushrooms have been highlighted as a rich and largely untapped source of biologically active compounds in both in vitro and in vivo neurodegenerative disease models, partially supported by successful clinical trial evaluations. Additionally, novel high-throughput methods for the screening of natural product compound libraries are being developed to help accelerate the neurodegenerative disease drug discovery process, targeting neuroinflammation. However, the breadth of research relating to mushroom natural product high-throughput screening is limited, providing an exciting opportunity for further detailed investigations.

Filtered Cerebrospinal Fluid From Patients With Amyotrophic Lateral Sclerosis Displays an Altered Proteome and Affects Motor Phenotype in a Mouse Model

INTRODUCTION

Cerebrospinal fluid (CSF) has been implicated in amyotrophic lateral sclerosis (ALS) due to its ability to spread inflammatory proteins throughout the nervous system. We hypothesized that filtration of the CSF could remove pathogenic proteins and prevent them from altering motor phenotypes in a mouse model.

METHODS

We filtered the CSF from 11 ALS patients via 100 kilodaltons (kD) molecular weight cut-off filters. We used mass spectrometry-based discovery proteomics workflows to compare protein abundances before and after filtration. To test the effects of CSF filtration on motor function, we injected groups of mice with saline, filtered ALS-CSF, or unfiltered ALS-CSF (n=12 per group) and assessed motor function via pole descent and open field tests.

RESULTS

We identified proteins implicated in ALS pathogenesis and showed that these were removed in significant amounts in our workflow. Key filtered proteins included complement proteins, chitinases, serine protease inhibitors, and neuro-inflammatory proteins such as amyloid precursor protein, chromogranin A, and glial fibrillary acidic protein. Compared to the filtered ALS-CSF mice, unfiltered ALS-CSF mice took longer to descend a pole (10 days post-injection, 11.14 seconds vs 14.25 seconds, p = 0.02) and explored less on an open field (one day post-injection, 21.81 m vs 16.83 m, p = 0.0004).

CONCLUSIONS

We demonstrated the ability to filter proteins from the CSF of ALS patients and identified potentially pathologic proteins that were reduced in quantity. Additionally, we demonstrated the ability of unfiltered ALS-CSF to induce motor deficits in mice on the pole descent and open field tests and showed that filtration could prevent this deficit. Given the lack of effective treatments for ALS, this could be a novel solution for patients suffering from this deadly and irreversible condition.

Praja1 RING-finger E3 ubiquitin ligase is a common suppressor of neurodegenerative disease-associated protein aggregation

The formation of misfolded protein aggregates is one of the pathological hallmarks of neurodegenerative diseases. We have previously demonstrated the cytoplasmic aggregate formation of adenovirally expressed transactivation response DNA-binding protein of 43 kDa (TDP-43), the main constituent of neuronal cytoplasmic aggregates in cases of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), in cultured neuronal cells under the condition of proteasome inhibition. The TDP-43 aggregate formation was markedly suppressed by co-infection of adenoviruses expressing heat shock transcription factor 1 (HSF1), a master regulator of heat shock response, and Praja1 RING-finger E3 ubiquitin ligase (PJA1) located downstream of the HSF1 pathway. In the present study, we examined other reportedly known E3 ubiquitin ligases for TDP-43, i.e. Parkin, RNF112 and RNF220, but failed to find their suppressive effects on neuronal cytoplasmic TDP-43 aggregate formation, although they all bind to TDP-43 as verified by co-immunoprecipitation. In contrast, PJA1 also binds to adenovirally expressed wild-type and mutated fused in sarcoma, superoxide dismutase 1, α-synuclein and ataxin-3, and huntingtin polyglutamine proteins in neuronal cultures and suppressed the aggregate formation of these proteins. These results suggest that PJA1 is a common sensing factor for aggregate-prone proteins to counteract their aggregation propensity, and could be a potential therapeutic target for neurodegenerative diseases that include ALS, FTLD, Parkinson's disease and polyglutamine diseases.

RNA-Binding Proteins as Epigenetic Regulators of Brain Functions and Their Involvement in Neurodegeneration

A central aspect of nervous system development and function is the post-transcriptional regulation of mRNA fate, which implies time- and site-dependent translation, in response to cues originating from cell-to-cell crosstalk. Such events are fundamental for the establishment of brain cell asymmetry, as well as of long-lasting modifications of synapses (long-term potentiation: LTP), responsible for learning, memory, and higher cognitive functions. Post-transcriptional regulation is in turn dependent on RNA-binding proteins that, by recognizing and binding brief RNA sequences, base modifications, or secondary/tertiary structures, are able to control maturation, localization, stability, and translation of the transcripts. Notably, most RBPs contain intrinsically disordered regions (IDRs) that are thought to be involved in the formation of membrane-less structures, probably due to liquid-liquid phase separation (LLPS). Such structures are evidenced as a variety of granules that contain proteins and different classes of RNAs. The other side of the peculiar properties of IDRs is, however, that, under altered cellular conditions, they are also prone to form aggregates, as observed in neurodegeneration. Interestingly, RBPs, as part of both normal and aggregated complexes, are also able to enter extracellular vesicles (EVs), and in doing so, they can also reach cells other than those that produced them.

In Vitro Interaction of a C-Terminal Fragment of TDP-43 Protein with Human Serum Albumin Modulates Its Aggregation

An increased level of naturally occurring anti-TDP-43 antibodies was observed in the serum and cerebrospinal fluid (CSF) of amyotrophic lateral sclerosis patients. Human serum albumin (HSA), the most abundant protein in blood plasma and CSF, is found to interact with pathological proteins like Aβ and α-synuclein. Therefore, we examined the effect on the in vitro aggregation of a C-terminal fragment of TDP-43 in the presence of HSA. We found that the lag phase in TDP-43^2C aggregation is abrogated in the presence of HSA, but there is an overall decreased aggregation as examined by thioflavin-T fluorescence spectroscopy and microscopy. An early onset of TDP-43^2C oligomer formation in the presence of HSA was observed using atomic force microscopy and transmission electron microscopy. Also, a known chemical inhibitor of TDP-43^2Caggregation, AIM4, abolishes the HSA-induced early formation of TDP-43^2C oligomers. Notably, the aggregates of TDP-43^2C formed in the presence of HSA are more stable against sarkosyl detergent. Using affinity copurification, we observed that HSA can bind to TDP-43^2C, and biolayer interferometry further supported their physical interaction and suggested the binding affinity to be in sub-micromolar range. Taken together, the data support that HSA can interact with TDP-43^2C in vitro and affect its aggregation.

Sertoli cells require TDP-43 to support spermatogenesis†

TAR DNA binding protein of 43 kD (TDP-43) is an evolutionarily conserved, ubiquitously expressed transcription factor and RNA-binding protein with major human health relevance. TDP-43 is present in Sertoli and germ cells of the testis and is aberrantly expressed in the sperm of infertile men. Sertoli cells play a key role in spermatogenesis by offering physical and nutritional support to male germ cells. The current study investigated the requirement of TDP-43 in Sertoli cells. Conditional knockout (cKO) of TDP-43 in mouse Sertoli cells caused failure of spermatogenesis and male subfertility. The cKO mice showed decreased testis weight, and low sperm count. Testis showed loss of germ cell layers, presence of vacuoles, and sloughing of round spermatids, suggesting loss of contact with Sertoli cells. Using a biotin tracer, we found that the blood-testis barrier (BTB) was disrupted as early as postnatal day 24 and worsened in adult cKO mice. We noted aberrant expression of the junction proteins connexin-43 (gap junction) and N-cadherin (ectoplasmic specialization). Oil Red O staining showed a decrease in lipid droplets (phagocytic function) in tubule cross-sections, Sertoli cells cytoplasm, and in the lumen of seminiferous tubules of cKO mice. Finally, qRT-PCR showed upregulation of genes involved in the formation and/or maintenance of Sertoli cell junctions as well as in the phagocytic pathway. Sertoli cells require TDP-43 for germ cell attachment, formation and maintenance of BTB, and phagocytic function, thus indicating an essential role for TDP-43 in the maintenance of spermatogenesis.

Distribution Features and Potential Effects of Serotonin in the Cerebrum of SOD1 G93A Transgenic Mice

Serotonin (5-HT) participates in the pathogenesis of amyotrophic lateral sclerosis (ALS), but its effects have not been completely clarified. Therefore, we observed the distribution features and potential effects of 5-HT in the cerebrum of G93A SOD1 transgenic (TG) and wild-type (WT) mice by fluorescence immunohistochemistry, Western blotting, ELISA, as well as motor function measurements. Both 5-HT and tryptophan hydroxylase-2 (TPH2) were mainly present in the limbic systems of the cerebrum, such as the glomerular layer of the olfactory bulb, nucleus accumbens, cingulate, fimbria of the hippocampus, mediodorsal thalamic nucleus, habenular nucleus, ventromedial hypothalamus nucleus, lateral hypothalamus area, dorsal raphe nucleus, and piriform cortex. TPH2 and 5-HT were expressed in cell bodies in the dorsal raphe nucleus and piriform cortex, while in other regions they were distributed as filaments and clump shapes in axons. The TPH2 distribution in the cerebrum of TG was significantly lower than that in WT in preset, onset, and progression stages. TPH2 expression in the fimbria of the hippocampus, mediodorsal thalamic nucleus, habenular nucleus, ventromedial hypothalamus nucleus and lateral hypothalamus area was increased in the onset stage and decreased in the progression stage, gradually decreased in the cingulate with disease progression and significantly decreased in the glomerular layer of the olfactory bulb and nucleus accumbens in the onset stage in TG. The number of mammalian achaete-scute homolog-1 in the subventricular zone (SVZ) in TG was significantly lower than that in WT, which was correlated with the TPH2 distribution. Double immunofluorescence staining showed that TPH2, mammalian achaete-scute homolog-1 and 5-HT were mainly expressed in neurons but rarely expressed in microglia or astrocytes in the piriform cortex. The relative fluorescence density of TPH2 in the cingulate region was negatively correlated with the disease severity. Our findings suggest that 5-HT plays a protective role in ALS, likely by regulating neural stem cells in the subventricular zone that might be involved in neuron development in the piriform cortex.

The Potential Role of Cytotoxic Immune Effectors in Induction, Progression and Pathogenesis of Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is an auto-immune neurodegenerative disorder affecting the motor-neuron system. The causes of ALS are heterogeneous, and are only partially understood. We studied different aspects of immune pathogenesis in ALS and found several basic mechanisms which are potentially involved in the disease. Our findings demonstrated that ALS patients' peripheral blood contains higher proportions of NK and B cells in comparison to healthy individuals. Significantly increased IFN-γ secretion by anti-CD3/28 mAbs-treated peripheral blood mononuclear cells (PBMCs) were observed in ALS patients, suggesting that hyper-responsiveness of T cell compartment could be a potential mechanism for ALS progression. In addition, elevated granzyme B and perforin secretion at a single cell level, and increased cytotoxicity and secretion of IFN-γ by patients' NK cells under specific treatment conditions were also observed. Increased IFN-γ secretion by ALS patients' CD8+ T cells in the absence of IFN-γ receptor expression, and increased CD8+ T cell effector/memory phenotype as well as increased granzyme B at the single cell level points to the CD8+ T cells as potential cells in targeting motor neurons. Along with the hyper-responsiveness of cytotoxic immune cells, significantly higher levels of inflammatory cytokines including IFN-γ was observed in peripheral blood-derived serum of ALS patients. Supernatants obtained from ALS patients' CD8+ T cells induced augmented cell death and differentiation of the epithelial cells. Weekly N-acetyl cysteine (NAC) infusion in patients decreased the levels of many inflammatory cytokines in peripheral blood of ALS patient except IFN-γ, TNF-α, IL-17a and GMCSF which remained elevated. Findings of this study indicated that CD8+ T cells and NK cells are likely culprits in targeting motor neurons and therefore, strategies should be designed to decrease their function, and eliminate the aggressive nature of these cells. Analysis of genetic mutations in ALS patient in comparison to identical twin revealed a number of differences and similarities which may be important in the pathogenesis of the disease.