Amyotrophic lateral sclerosis: update and new developments

Downregulation of Lnc-ABCA12-3 modulates UBQLN1 expression and protein homeostasis pathways in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by motor neuron degeneration. Dysregulation of long non-coding RNAs (lncRNAs) has been implicated in ALS pathogenesis but their roles remain unclear. Previous studies found lnc-ABCA12-3 was downregulated in ALS patients. We aim to characterize the expression and function of lnc-ABCA12-3 in ALS and explore its mechanisms of action. Lnc-ABCA12-3 expression was analyzed in PBMCs from ALS patients and correlated with clinical outcomes. Effect of modulating lnc-ABCA12-3 expression was assessed in cell models using assays of apoptosis, protein homeostasis and pathway analysis. RNA pull-down and interaction studies were performed to identify lnc-ABCA12-3 binding partners. Lnc-ABCA12-3 was downregulated in ALS patients, correlating with faster progression and shorter survival. Overexpression of lnc-ABAC12-3 conferred protection against oxidative stress-induced apoptosis, while knockdown lnc-ABCA12-3 enhanced cell death. Lnc-ABCA12-3 maintained protein quality control pathways, including ubiquitination, autophagy and stress granule formation, by regulating the ubiquitin shuttle protein UBQLN1. This study identified lnc-ABCA12-3 as a novel regulatory lncRNA implicated in ALS pathogenesis by modulating cellular survival and stress responses through interactions with UBQLN1, influencing disease progression. Lnc-ABCA12-3 may influence ALS through regulating protein homeostasis pathways.

Role of miRNAs in Neurodegeneration: From Disease Cause to Tools of Biomarker Discovery and Therapeutics

Neurodegenerative diseases originate from neuronal loss in the central nervous system (CNS). These debilitating diseases progress with age and have become common due to an increase in longevity. The National Institute of Environmental Health Science’s 2021 annual report suggests around 6.2 million Americans are living with Alzheimer’s disease, and there is a possibility that there will be 1.2 million Parkinson’s disease patients in the USA by 2030. There is no clear-cut universal mechanism for identifying neurodegenerative diseases, and therefore, they pose a challenge for neurobiology scientists. Genetic and environmental factors modulate these diseases leading to familial or sporadic forms. Prior studies have shown that miRNA levels are altered during the course of the disease, thereby suggesting that these noncoding RNAs may be the contributing factor in neurodegeneration. In this review, we highlight the role of miRNAs in the pathogenesis of neurodegenerative diseases. Through this review, we aim to achieve four main objectives: First, we highlight how dysregulation of miRNA biogenesis led to these diseases. Second, we highlight the computational or bioinformatics tools required to identify the putative molecular targets of miRNAs, leading to biological molecular pathways or mechanisms involved in these diseases. Third, we focus on the dysregulation of miRNAs and their target genes leading to several neurodegenerative diseases. In the final section, we highlight the use of miRNAs as potential diagnostic biomarkers in the early asymptomatic preclinical diagnosis of these age-dependent debilitating diseases. Additionally, we discuss the challenges and advances in the development of miRNA therapeutics for brain targeting. We list some of the innovative strategies employed to deliver miRNA into target cells and the relevance of these viral and non-viral carrier systems in RNA therapy for neurodegenerative diseases. In summary, this review highlights the relevance of studying brain-enriched miRNAs, the mechanisms underlying their regulation of target gene expression, their dysregulation leading to progressive neurodegeneration, and their potential for biomarker marker and therapeutic intervention. This review thereby highlights ways for the effective diagnosis and prevention of these neurodegenerative disorders in the near future.

Amyotrophic Lateral Sclerosis (ALS): Stressed by Dysfunctional Mitochondria-Endoplasmic Reticulum Contacts (MERCs)

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which there is currently no cure. Progress in the characterization of other neurodegenerative mechanisms has shifted the spotlight onto an intracellular structure called mitochondria-endoplasmic reticulum (ER) contacts (MERCs) whose ER portion can be biochemically isolated as mitochondria-associated membranes (MAMs). Within the central nervous system (CNS), these structures control the metabolic output of mitochondria and keep sources of oxidative stress in check via autophagy. The most relevant MERC controllers in the ALS pathogenesis are vesicle-associated membrane protein-associated protein B (VAPB), a mitochondria-ER tether, and the ubiquitin-specific chaperone valosin containing protein (VCP). These two systems cooperate to maintain mitochondrial energy output and prevent oxidative stress. In ALS, mutant VAPB and VCP take a central position in the pathology through MERC dysfunction that ultimately alters or compromises mitochondrial bioenergetics. Intriguingly, both proteins are targets themselves of other ALS mutant proteins, including C9orf72, FUS, or TDP-43. Thus, a new picture emerges, where different triggers cause MERC dysfunction in ALS, subsequently leading to well-known pathological changes including endoplasmic reticulum (ER) stress, inflammation, and motor neuron death.

Emerging Evidence Highlighting the Importance of Redox Dysregulation in the Pathogenesis of Amyotrophic Lateral Sclerosis (ALS)

The cellular redox state, or balance between cellular oxidation and reduction reactions, serves as a vital antioxidant defence system that is linked to all important cellular activities. Redox regulation is therefore a fundamental cellular process for aerobic organisms. Whilst oxidative stress is well described in neurodegenerative disorders including amyotrophic lateral sclerosis (ALS), other aspects of redox dysfunction and their contributions to pathophysiology are only just emerging. ALS is a fatal neurodegenerative disease affecting motor neurons, with few useful treatments. Hence there is an urgent need to develop more effective therapeutics in the future. Here, we discuss the increasing evidence for redox dysregulation as an important and primary contributor to ALS pathogenesis, which is associated with multiple disease mechanisms. Understanding the connection between redox homeostasis, proteins that mediate redox regulation, and disease pathophysiology in ALS, may facilitate a better understanding of disease mechanisms, and lead to the design of better therapeutic strategies.

A Systematic and Comprehensive Review on Disease-Causing Genes in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder and is characterized by degeneration and axon loss from the upper motor neuron, that descends from the lower motor neuron in the brain. Over the period, assorted outcomes from medical findings, molecular pathogenesis, and structural and biophysical studies have abetted in providing thoughtful insights underlying the importance of disease-causing genes in ALS. Consequently, numerous mechanisms were proposed for the pathogenesis of ALS, considering protein mutations, aggregation, and misfolding. Besides, the answers to the majority of ALS cases that happen to be sporadic still remain obscure. The application in discovering susceptibility factors in ALS contemplating the genetic factors is to be further dissevered in the future years with innovation in research studies. Hence, this review targets in revisiting the breakthroughs on the disease-causing genes related with ALS.

Amyotrophic Lateral Sclerosis: A Neurodegenerative Motor Neuron Disease With Ocular Involvement

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that causes degeneration of the lower and upper motor neurons and is the most prevalent motor neuron disease. This disease is characterized by muscle weakness, stiffness, and hyperreflexia. Patients survive for a short period from the onset of the disease. Most cases are sporadic, with only 10% of the cases being genetic. Many genes are now known to be involved in familial ALS cases, including some of the sporadic cases. It has also been observed that, in addition to genetic factors, there are numerous molecular mechanisms involved in these pathologies, such as excitotoxicity, mitochondrial disorders, alterations in axonal transport, oxidative stress, accumulation of misfolded proteins, and neuroinflammation. This pathology affects the motor neurons, the spinal cord, the cerebellum, and the brain, but recently, it has been shown that it also affects the visual system. This impact occurs not only at the level of the oculomotor system but also at the retinal level, which is why the retina is being proposed as a possible biomarker of this pathology. The current review discusses the main aspects mentioned above related to ALS, such as the main genes involved, the most important molecular mechanisms that affect this pathology, its ocular involvement, and the possible usefulness of the retina as a biomarker.

Salivary Biomarkers: Future Approaches for Early Diagnosis of Neurodegenerative Diseases

Many neurological diseases are characterized by progressive neuronal degeneration. Early diagnosis and new markers are necessary for prompt therapeutic intervention. Several studies have aimed to identify biomarkers in different biological liquids. Furthermore, it is being considered whether saliva could be a potential biological sample for the investigation of neurodegenerative diseases. This work aims to provide an overview of the literature concerning biomarkers identified in saliva for the diagnosis of neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Specifically, the studies have revealed that is possible to quantify beta-amyloid_1–42 and TAU protein from the saliva of AD patients. Instead, alpha-synuclein and protein deglycase (DJ-1) have been identified as new potential salivary biomarkers for the diagnosis of PD. Nevertheless, future studies will be needed to validate these salivary biomarkers in the diagnosis of neurological diseases.

Intravenously Administered, Retinoid Activating Nanoparticles Increase Lifespan and Reduce Neurodegeneration in the SOD1G93A Mouse Model of ALS

Dysregulation of the retinoic acid (RA) signaling pathway is observed in amyotrophic lateral sclerosis (ALS) and other neurodegenerative disorders. Here, we investigated the therapeutic potential of retinoid activation via the RA receptor β (RARβ) in the SOD1^G93A mouse model of ALS. Our approach utilized the RARβ agonist adapalene, which we previously found to be neuroprotective in vitro. Adapalene, like most retinoids, is poorly water soluble, which has thus far prevented effective drug delivery in vivo. To address this challenge, we encapsulated adapalene within nanoparticles (Adap-NPs) composed of poly(lactic acid)-poly(ethylene glycol) (PLA-PEG). Our data demonstrate that intravenous administration of Adap-NPs robustly activates retinoid signaling in the CNS. Chronic administration of Adap-NPs resulted in improved motor performance, prolonged lifespan, and neuroprotection in SOD1^G93A mice. This study highlights retinoid signaling as a valuable therapeutic approach and presents a novel nanoparticle platform for the treatment of ALS.

Changes in Retinal OCT and Their Correlations with Neurological Disability in Early ALS Patients, a Follow-Up Study

BACKGROUND

To compare early visual changes in amyotrophic lateral sclerosis (ALS) patients with healthy controls in a baseline exploration, to follow-up the patients after 6 months, and to correlate these visual changes with neurological disability.

METHODS

All patients underwent a comprehensive neurological and ophthalmological examination. A linear mixed analysis and Bonferroni p-value correction were performed, testing four comparisons as follows: Control baseline vs. control follow-up, control baseline vs. ALS baseline, control follow-up vs. ALS follow-up, and ALS baseline vs. ALS follow-up.

RESULTS

The mean time from the diagnosis was 10.80 ± 5.5 months. The analysis of the optical coherence tomography (OCT) showed: (1) In ALS baseline vs. control baseline, a macular significantly increased thickness of the inner macular ring temporal and inferior areas; (2) in ALS follow-up vs. ALS baseline, a significant macular thinning in the inner and outer macular ring inferior areas; (3) in ALS follow-up vs. ALS baseline, a significant peripapillary retinal nerve fiber layer (pRNFL) thinning in the superior and inferior quadrants; and (4) ALS patients showed a moderate correlation between some OCT pRNFL parameters and Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) score.

CONCLUSION

The OCT showed retinal changes in patients with motoneuron disease and could serve as a complementary tool for studying ALS.

Potential for therapeutic use of hydrogen sulfide in oxidative stress-induced neurodegenerative diseases

Oxidative phosphorylation is a source of energy production by which many cells satisfy their energy requirements. Endogenous reactive oxygen species (ROS) are by-products of oxidative phosphorylation. ROS are formed due to the inefficiency of oxidative phosphorylation, and lead to oxidative stress that affects mitochondrial metabolism. Chronic oxidative stress contributes to the onset of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). The immediate consequences of oxidative stress include lipid peroxidation, protein oxidation, and mitochondrial deoxyribonucleic acid (mtDNA) mutation, which induce neuronal cell death. Mitochondrial binding of amyloid-β (Aβ) protein has been identified as a contributing factor in AD. In PD and HD, respectively, α-synuclein (α-syn) and huntingtin (Htt) gene mutations have been reported to exacerbate the effects of oxidative stress. Similarly, abnormalities in mitochondrial dynamics and the respiratory chain occur in ALS due to dysregulation of mitochondrial complexes II and IV. However, oxidative stress-induced dysfunctions in neurodegenerative diseases can be mitigated by the antioxidant function of hydrogen sulfide (H2S), which also acts through the potassium (KATP/K+) ion channel and calcium (Ca2+) ion channels to increase glutathione (GSH) levels. The pharmacological activity of H2S is exerted by both inorganic and organic compounds. GSH, glutathione peroxidase (Gpx), and superoxide dismutase (SOD) neutralize H2O2-induced oxidative damage in mitochondria. The main purpose of this review is to discuss specific causes and effects of mitochondrial oxidative stress in neurodegenerative diseases, and how these are impacted by the antioxidant functions of H2S to support the development of advancements in neurodegenerative disease treatment.

EWSR1, a multifunctional protein, regulates cellular function and aging via genetic and epigenetic pathways

Ewing's sarcoma (EWS) is a bone cancer arising predominantly in young children. EWSR1 (Ewing Sarcoma breakpoint region 1/EWS RNA binding protein 1) gene is ubiquitously expressed in most cell types, indicating it has diverse roles in various cellular processes and organ development. Recently, several studies have shown that missense mutations of EWSR1 genes are known to be associated with central nervous system disorders such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Otherwise, EWSR1 plays epigenetic roles in gene expression, RNA processing, and cellular signal transduction. Interestingly, EWSR1 controls micro RNA (miRNA) levels via Drosha, leading to autophagy dysfunction and impaired dermal development. Ewsr1 deficiency also leads to premature senescence of blood cells and gamete cells with a high rate of apoptosis due to the abnormal meiosis. Despite these roles of EWSR1 in various cellular functions, the exact mechanisms are not yet understood. In this context, the current review overviews a large body of evidence and discusses on what EWSR1 genetic mutations are associated with brain diseases and on how EWSR1 modulates cellular function via the epigenetic pathway. This will provide a better understanding of bona fide roles of EWSR1 in aging and its association with brain disorders.

Overview of Impaired BDNF Signaling, Their Coupled Downstream Serine-Threonine Kinases and SNARE/SM Complex in the Neuromuscular Junction of the Amyotrophic Lateral Sclerosis Model SOD1-G93A Mice

Amyotrophic lateral sclerosis (ALS) is a chronic neurodegenerative disease characterized by progressive motor weakness. It is accepted that it is caused by motoneuron degeneration leading to a decrease in muscle stimulation. However, ALS is being redefined as a distal axonopathy, in that neuromuscular junction dysfunction precedes and may even influence motoneuron loss. In this synapse, several metabotropic receptor-mediated signaling pathways converge on effector kinases that phosphorylate targets that are crucial for synaptic stability and neurotransmission quality. We have previously shown that, in physiological conditions, nerve-induced muscle contraction regulates the brain-derived neurotrophic factor/tropomyosin-related kinase B (BDNF/TrkB) signaling to retrogradely modulate presynaptic protein kinases PKC and PKA, which are directly involved in the modulation of acetylcholine release. In ALS patients, the alteration of this signaling may significantly contribute to a motor impairment. Here, we investigate whether BDNF/TrkB signaling, the downstream PKC (cPKCβI, cPKCα, and nPKCε isoforms), and PKA (regulatory and catalytic subunits) and some SNARE/SM exocytotic machinery proteins (Munc18-1 and SNAP-25) are altered in the skeletal muscle of pre- and symptomatic SOD1-G93A mice. We found that this pathway is strongly affected in symptomatic ALS mice muscles including an unbalance between (I) BDNF and TrkB isoforms, (II) PKC isoforms and PKA subunits, and (III) Munc18-1 and SNAP-25 phosphorylation ratios. Changes in TrkB.T1 and cPKCβI are precociously observed in presymptomatic mice. Altogether, several of these molecular alterations can be partly associated with the known fast-to-slow motor unit transition during the disease process but others can be related with the initial disease pathogenesis.

Mesenchymal Stem Cells: A Potential Therapeutic Approach for Amyotrophic Lateral Sclerosis?

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the degeneration of both upper and lower motor neurons. Patients show both motor and extra-motor symptoms. A cure is not available at this time, and the disease leads to death within 3-5 years, mainly due to respiratory failure. Stem cell therapy is arising as a new promising approach for the treatment of neurodegenerative disorders. In particular, mesenchymal stem cells (MSCs) seem the most suitable type of stem cells, thanks to their demonstrated beneficial effects in different experimental models, to the easy availability, and to the lack of ethical problems. In this review, we focused on the studies involving ALS rodent models and clinical trials in order to understand the potential beneficial effects of MSC transplantation. In different ALS rodent models, the administration of MSCs induced a delay in disease progression and at least a partial recovery of the motor function. In addition, clinical trials evidenced the feasibility and safety of MSC transplantation in ALS patients, given that no major adverse events were recorded. However, only partial improvements were shown. For this reason, more studies and trials are needed to clarify the real effectiveness of MSC-based therapy in ALS.

Transplantation of human bone marrow stem cells into symptomatic ALS mice enhances structural and functional blood-spinal cord barrier repair

Accumulating evidence shows alterations in the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB) in ALS patients and in animal models of disease, mainly by endothelial cell (EC) damage. Repair of the altered barrier in the CNS by replacement of ECs via cell transplantation may be a new therapeutic approach for ALS. Recently, we demonstrated positive effects towards BSCB repair by intravenous administration of unmodified human bone marrow CD34⁺ (hBM34⁺) cells at different doses into symptomatic ALS mice. However, particular benefits of these transplanted cells on microvascular integrity in symptomatic ALS mice are still unclear. The aim of the present study was to determine the structural and functional spinal cord capillary integrity in symptomatic ALS mice after intravenous administration of hBM34⁺ cells. The G93A mice at 13 weeks of age intravenously received one of three different cell doses (5 × 10⁴, 5 × 10⁵, or 1 × 10⁶) and were euthanized at 17 weeks of age (4 weeks post-transplant). Control groups were media-treated and non-carrier mutant SOD1 gene mice. Capillary ultrastructural (electron microscopy), immunohistochemical (laminin and HuNu), and histological (myelin and capillary density) analyses were performed in the cervical and lumbar spinal cords. Capillary permeability in the spinal cords was determined by Evans Blue (EB) injection. Results showed significant restoration of ultrastructural capillary morphology, improvement of basement membrane integrity, enhancement of axonal myelin coherence, and stabilization of capillary density in the spinal cords primarily of ALS mice receiving the high dose of 1 × 10⁶ cells. Moreover, substantial reduction of parenchymal EB levels was determined in these mice, confirming our previous results on capillary permeability. Additionally, transplanted cells were detected in blood smears of sacrificed late symptomatic mice by HuNu marker. Altogether, these results provide novel evidence that unmodified bone marrow hematopoietic stem cell treatment at optimal dose might be beneficial for structural and functional repair of the damaged BSCB in advanced stage of ALS, potentially resulting in delayed disease progression by increased motor neuron survival.

Potential Role of Humoral IL-6 Cytokine in Mediating Pro-Inflammatory Endothelial Cell Response in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a multifactorial disease with limited therapeutic options. Numerous intrinsic and extrinsic factors are involved in ALS motor neuron degeneration. One possible effector accelerating motor neuron death in ALS is damage to the blood-Central Nervous System barrier (B-CNS-B), mainly due to endothelial cell (EC) degeneration. Although mechanisms of EC damage in ALS are still unknown, vascular impairment may be initiated by various humoral inflammatory factors and other mediators. Systemic IL-6-mediated inflammation is a possible early extrinsic effector leading to the EC death causing central nervous system (CNS) barrier damage. In this review, we discuss the potential role of humoral factors in triggering EC alterations in ALS. A specific focus was on humoral IL-6 cytokine mediating EC inflammation via the trans-signaling pathway. Our preliminary in vitro studies demonstrated a proof of principle that short term exposure of human bone marrow endothelial cells to plasma from ALS patient leads to cell morphological changes, significantly upregulated IL-6R immunoexpression, and pro-inflammatory cell response. Our in-depth understanding of specific molecular mechanisms of this humoral cytokine in EC degeneration may facilitate an endothelial-IL-6-targeting therapy for restoring cell homeostasis and eventually reestablishing B-CNS-B integrity in ALS.

ALS Associated Mutations in Matrin 3 Alter Protein-Protein Interactions and Impede mRNA Nuclear Export

Mutations in Matrin 3 have recently been linked to ALS, though the mechanism that induces disease in these patients is unknown. To define the protein interactome of wild-type and ALS-linked MATR3 mutations, we performed immunoprecipitation followed by mass spectrometry using NSC-34 cells expressing human wild-type or mutant Matrin 3. Gene ontology analysis identified a novel role for Matrin 3 in mRNA transport centered on proteins in the TRanscription and EXport (TREX) complex, known to function in mRNA biogenesis and nuclear export. ALS-linked mutations in Matrin 3 led to its re-distribution within the nucleus, decreased co-localization with endogenous Matrin 3 and increased co-localization with specific TREX components. Expression of disease-causing Matrin 3 mutations led to nuclear mRNA export defects of both global mRNA and more specifically the mRNA of TDP-43 and FUS. Our findings identify a potential pathogenic mechanism attributable to MATR3 mutations and further link cellular transport defects to ALS.

Riluzole: real-world evidence supports significant extension of median survival times in patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is the commonest form of motor neuron disease and is a fatal, degenerative, multisystem disorder affecting upper and/or lower motor neurons in the motor cortex, brain stem, and spinal cord. ALS is characterized by progressive atrophy of associated bulbar, limb, thoracic, and abdominal muscles and supporting cells manifesting in a range of muscular symptoms such as weakness and wasting and eventual paralysis; the majority of patients will die from respiratory failure within 2–5 years of onset. Riluzole, a synthetic benzothiazole drug with glutamine antagonist activity, is indicated for the treatment of patients with ALS and is the only drug that has been shown to slow the course of the disease and extend survival in ALS patients. The original analyses, and subsequent meta-analyses, of data obtained from randomized controlled trials (RCTs) suggest that riluzole typically extends survival by 2–3 months and increases the chance of an additional year of survival by ~9%. However, published real-world evidence (RWE) from 10 clinical ALS databases indicates that riluzole therapy may afford much greater extension of survival, and improvements in median survival times of more than 19 months have been reported in the overall ALS patient population. This article will review the available data from RCTs and RWE on riluzole therapy.

ALS Pathogenesis and Therapeutic Approaches: The Role of Mesenchymal Stem Cells and Extracellular Vesicles

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive muscle paralysis determined by the degeneration of motoneurons in the motor cortex brainstem and spinal cord. The ALS pathogenetic mechanisms are still unclear, despite the wealth of studies demonstrating the involvement of several altered signaling pathways, such as mitochondrial dysfunction, glutamate excitotoxicity, oxidative stress and neuroinflammation. To date, the proposed therapeutic strategies are targeted to one or a few of these alterations, resulting in only a minimal effect on disease course and survival of ALS patients. The involvement of different mechanisms in ALS pathogenesis underlines the need for a therapeutic approach targeted to multiple aspects. Mesenchymal stem cells (MSC) can support motoneurons and surrounding cells, reduce inflammation, stimulate tissue regeneration and release growth factors. On this basis, MSC have been proposed as promising candidates to treat ALS. However, due to the drawbacks of cell therapy, the possible therapeutic use of extracellular vesicles (EVs) released by stem cells is raising increasing interest. The present review summarizes the main pathological mechanisms involved in ALS and the related therapeutic approaches proposed to date, focusing on MSC therapy and their preclinical and clinical applications. Moreover, the nature and characteristics of EVs and their role in recapitulating the effect of stem cells are discussed, elucidating how and why these vesicles could provide novel opportunities for ALS treatment.

Current Therapy of Drugs in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS), commonly termed as motor neuron disease (MND) in UK, is a chronically lethal disorder among the neurodegenerative diseases, meanwhile. ALS is basically irreversible and progressive deterioration of upper and lower motor neurons in the motor cortex, brain stem and medulla spinalis. Riluzole, used for the treatment of ALS, was demonstrated to slightly delay the initiation of respiratory dysfunction and extend the median survival of patients by a few months. In this study, the key biochemical defects were discussed, such as: mutant Cu/Zn superoxide dismutase, mitochondrial protectants, and anti-excitotoxic/ anti-oxidative / anti-inflammatory/ anti-apoptotic agents, so the related drug candidates that have been studied in ALS models would possibly be further used in ALS patients.

Astrocytes drive upregulation of the multidrug resistance transporter ABCB1 (P-Glycoprotein) in endothelial cells of the blood-brain barrier in mutant superoxide dismutase 1-linked amyotrophic lateral sclerosis

The efficacy of drugs targeting the CNS is influenced by their limited brain access, which can lead to complete pharmacoresistance. Recently a tissue-specific and selective upregulation of the multidrug efflux transporter ABCB1 or P-glycoprotein (P-gp) in the spinal cord of both patients and the mutant SOD1-G93A mouse model of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease that prevalently kills motor neurons has been reported. Here, we extended the analysis of P-gp expression in the SOD1-G93A ALS mouse model and found that P-gp upregulation was restricted to endothelial cells of the capillaries, while P-gp expression was not detected in other cells of the spinal cord parenchyma such as astrocytes, oligodendrocytes, and neurons. Using both in vitro human and mouse models of the blood-brain barrier (BBB), we found that mutant SOD1 astrocytes were driving P-gp upregulation in endothelial cells. In addition, a significant increase in reactive oxygen species production, Nrf2 and NFκB activation in endothelial cells exposed to mutant SOD1 astrocytes in both human and murine BBB models were observed. Most interestingly, astrocytes expressing FUS-H517Q, a different familial ALS-linked mutated gene, also drove NFκB-dependent upregulation of P-gp. However, the pathway was not dependent on oxidative stress but rather involved TNF-α release. Overall, these findings indicated that nuclear translocation of NFκB was a converging mechanism used by endothelial cells of the BBB to upregulate P-gp expression in mutant SOD1-linked ALS and possibly other forms of familial ALS. GLIA 2016 GLIA 2016;64:1298-1313.

Two mutations G335D and Q343R within the amyloidogenic core region of TDP-43 influence its aggregation and inclusion formation

TDP-43 is a DNA/RNA binding protein associated with TDP-43 proteinopathies. Many mutations have been identified in the flexible C-terminal region, which is implicated in the disease pathology. We investigated four point mutations in the amyloidogenic core region (residues 311–360) of TDP-43 by biochemical and spectroscopic methods. We found that the G335D mutation enhances the aggregation and inclusion formation of TDP-43 and this mutant in TDP-35 (the C-terminal fragment of 35 kDa) exaggerates the antagonist effect on RNA processing by endogenous TDP-43; whereas Q343R gives an opposite effect. As a comparison, M337V and Q331K have very little impact on the aggregation and inclusion formation of TDP-43 or TDP-35. NMR structural analysis showed that the G335D mutant in the core region forms a loop linker between the two α-helices and promotes α-to-β transition, but Q343R loses the second helix and consequently the structural transformation. Thus, the propensity of structural transformation in the amyloidogenic core of TDP-43 determines its aggregation and inclusion formation. This study may provide a molecular mechanism of the TDP-43 proteinopathies caused by genetic mutations.

Mice Overexpressing Both Non-Mutated Human SOD1 and Mutated SOD1(G93A) Genes: A Competent Experimental Model for Studying Iron Metabolism in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by degeneration and loss of motor neurons in the spinal cord, brainstem and motor cortex. Up to 10% of ALS cases are inherited (familial, fALS) and associated with mutations, frequently in the superoxide dismutase 1 (SOD1) gene. Rodent transgenic models of ALS are often used to elucidate a complex pathogenesis of this disease. Of importance, both ALS patients and animals carrying mutated human SOD1 gene show symptoms of oxidative stress and iron metabolism misregulation. The aim of our study was to characterize changes in iron metabolism in one of the most commonly used models of ALS – transgenic mice overexpressing human mutated SOD1^G93A gene. We analyzed the expression of iron-related genes in asymptomatic, 2-month-old and symptomatic, 4-month-old SOD1^G93A mice. In parallel, respective age-matched mice overexpressing human non-mutated SOD1 transgene and control mice were analyzed. We demonstrate that the overexpression of both SOD1 and SOD1^G93A genes account for a substantial increase in SOD1 protein levels and activity in selected tissues and that not all the changes in iron metabolism genes expression are specific for the overexpression of the mutated form of SOD1.

Regulation of ABC efflux transporters at blood-brain barrier in health and neurological disorders

The strength of the blood-brain barrier (BBB) in providing protection to the central nervous system from exposure to circulating chemicals is maintained by tight junctions between endothelial cells and by a broad range of transporter proteins that regulate exchange between CNS and blood. The most important transporters that restrict the permeability of large number of toxins as well as therapeutic agents are the ABC transporters. Among them, P-gp, BCRP, MRP1 and MRP2 are the utmost studied. These efflux transporters are neuroprotective, limiting the brain entry of neurotoxins; however, they could also restrict the entry of many therapeutics and contribute to CNS pharmacoresistance. Characterization of several regulatory pathways that govern expression and activity of ABC efflux transporters in the endothelium of brain capillaries have led to an emerging consensus that these processes are complex and contain several cellular and molecular elements. Alterations in ABC efflux transporters expression and/or activity occur in several neurological diseases. Here, we review the signaling pathways that regulate expression and transport activity of P-gp, BCRP, MRP1 and MRP2 as well as how their expression/activity changes in neurological diseases. This article is part of a Special Issue entitled SI: Neuroprotection.

NOX2 As a Target for Drug Development: Indications, Possible Complications, and Progress

SIGNIFICANCE

NOX2 is important for host defense, and yet is implicated in a large number of diseases in which inflammation plays a role in pathogenesis. These include acute and chronic lung inflammatory diseases, stroke, traumatic brain injury, and neurodegenerative diseases, including Alzheimer's and Parkinson's Diseases.

RECENT ADVANCES

Recent drug development programs have targeted several NOX isoforms that are implicated in a variety of diseases. The focus has been primarily on NOX4 and NOX1 rather than on NOX2, due, in part, to concerns about possible immunosuppressive side effects. Nevertheless, NOX2 clearly contributes to the pathogenesis of many inflammatory diseases, and its inhibition is predicted to provide a novel therapeutic approach.

CRITICAL ISSUES

Possible side effects that might arise from targeting NOX2 are discussed, including the possibility that such inhibition will contribute to increased infections and/or autoimmune disorders. The state of the field with regard to existing NOX2 inhibitors and targeted development of novel inhibitors is also summarized.

FUTURE DIRECTIONS

NOX2 inhibitors show particular promise for the treatment of inflammatory diseases, both acute and chronic. Theoretical side effects include pro-inflammatory and autoimmune complications and should be considered in any therapeutic program, but in our opinion, available data do not indicate that they are sufficiently likely to eliminate NOX2 as a drug target, particularly when weighed against the seriousness of many NOX2-related indications. Model studies demonstrating efficacy with minimal side effects are needed to encourage future development of NOX2 inhibitors as therapeutic agents.

Copper-based pulsed dipolar ESR spectroscopy as a probe of protein conformation linked to disease states

We demonstrate the ability of pulsed dipolar electron spin resonance (ESR) spectroscopy (PDS) to report on the conformation of Cu-Zn superoxide dismutase (SOD1) through the sensitive measurement of dipolar interactions between inherent Cu(2+) ions. Although the extent and the anisotropy of the Cu ESR spectrum provides challenges for PDS, Ku-band (17.3 GHz) double electron-electron resonance and double-quantum coherence variants of PDS coupled with distance reconstruction methods recover Cu-Cu distances in good agreement with crystal structures. Moreover, Cu-PDS measurements expose distinct differences between the conformational properties of wild-type SOD1 and a single-residue variant (I149T) that leads to the disease amyotrophic lateral sclerosis (ALS). The I149T protein displays a broader Cu-Cu distance distribution within the SOD1 dimer compared to wild-type. In a nitroxide (NO)-labeled sample, distance distributions obtained from Cu-Cu, Cu-NO, and NO-NO separations reveal increased structural heterogeneity within the protein and a tendency for mutant dimers to associate. In contrast, perturbations caused by the ALS mutation are completely masked in the crystal structure of I149T. Thus, PDS readily detects alterations in metalloenzyme solution properties not easily deciphered by other methods and in doing so supports the notion that increased range of motion and associations of SOD1 ALS variants contribute to disease progression.

RBM45 Modulates the Antioxidant Response in Amyotrophic Lateral Sclerosis through Interactions with KEAP1

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective loss of motor neurons. Various factors contribute to the disease, including RNA binding protein dysregulation and oxidative stress, but their exact role in pathogenic mechanisms remains unclear. We have recently linked another RNA binding protein, RBM45, to ALS via increased levels of protein in the cerebrospinal fluid of ALS patients and its localization to cytoplasmic inclusions in ALS motor neurons. Here we show RBM45 nuclear exit in ALS spinal cord motor neurons compared to controls, a phenotype recapitulated in vitro in motor neurons treated with oxidative stressors. We find that RBM45 binds and stabilizes KEAP1, the inhibitor of the antioxidant response transcription factor NRF2. ALS lumbar spinal cord lysates similarly show increased cytoplasmic binding of KEAP1 and RBM45. Binding of RBM45 to KEAP1 impedes the protective antioxidant response, thus contributing to oxidative stress-induced cellular toxicity. Our findings thus describe a novel link between a mislocalized RNA binding protein implicated in ALS (RBM45) and dysregulation of the neuroprotective antioxidant response seen in the disease.

Genotype-property patient-phenotype relations suggest that proteome exhaustion can cause amyotrophic lateral sclerosis

Late-onset neurodegenerative diseases remain poorly understood as search continues for the perceived pathogenic protein species. Previously, variants in Superoxide Dismutase 1 (SOD1) causing Amyotrophic Lateral Sclerosis (ALS) were found to destabilize and reduce net charge, suggesting a pathogenic aggregation mechanism. This paper reports analysis of compiled patient data and experimental and computed protein properties for variants of human SOD1, a major risk factor of ALS. Both stability and reduced net charge correlate significantly with disease, with larger significance than previously observed. Using two independent methods and two data sets, a probability < 3% (t-statistical test) is found that ALS-causing mutations share average stability with all possible 2907 SOD1 mutations. Most importantly, un-weighted patient survival times correlate strongly with the misfolded/unfolded protein copy number, expressed as an exponential function of the experimental stabilities (R² = 0.31, p = 0.002), and this phenotype is further aggravated by charge (R² = 0.51, p = 1.8 x 10−5). This finding suggests that disease relates to the copy number of misfolded proteins. Exhaustion of motor neurons due to expensive protein turnover of misfolded protein copies is consistent with the data but can further explain e.g. the expression-dependence of SOD1 pathogenicity, the lack of identification of a molecular toxic mode, elevated SOD1 mRNA levels in sporadic ALS, bioenergetic effects and increased resting energy expenditure in ALS patients, genetic risk factors affecting RNA metabolism, and recent findings that a SOD1 mutant becomes toxic when proteasome activity is recovered after washout of a proteasome inhibitor. Proteome exhaustion is also consistent with energy-producing mitochondria accumulating at the neuromuscular junctions where ALS often initiates. If true, this exhaustion mechanism implies a complete change of focus in treatment of ALS towards actively nursing the energy state and protein turnover of the motor neurons.

Aggregation propensities of superoxide dismutase G93 hotspot mutants mirror ALS clinical phenotypes

Protein framework alterations in heritable Cu, Zn superoxide dismutase (SOD) mutants cause misassembly and aggregation in cells affected by the motor neuron disease ALS. However, the mechanistic relationship between superoxide dismutase 1 (SOD1) mutations and human disease is controversial, with many hypotheses postulated for the propensity of specific SOD mutants to cause ALS. Here, we experimentally identify distinguishing attributes of ALS mutant SOD proteins that correlate with clinical severity by applying solution biophysical techniques to six ALS mutants at human SOD hotspot glycine 93. A small-angle X-ray scattering (SAXS) assay and other structural methods assessed aggregation propensity by defining the size and shape of fibrillar SOD aggregates after mild biochemical perturbations. Inductively coupled plasma MS quantified metal ion binding stoichiometry, and pulsed dipolar ESR spectroscopy evaluated the Cu(2+) binding site and defined cross-dimer copper-copper distance distributions. Importantly, we find that copper deficiency in these mutants promotes aggregation in a manner strikingly consistent with their clinical severities. G93 mutants seem to properly incorporate metal ions under physiological conditions when assisted by the copper chaperone but release copper under destabilizing conditions more readily than the WT enzyme. Altered intradimer flexibility in ALS mutants may cause differential metal retention and promote distinct aggregation trends observed for mutant proteins in vitro and in ALS patients. Combined biophysical and structural results test and link copper retention to the framework destabilization hypothesis as a unifying general mechanism for both SOD aggregation and ALS disease progression, with implications for disease severity and therapeutic intervention strategies.

Nuclear TAR DNA-binding protein 43: A new target for amyotrophic lateral sclerosis treatment

Abnormal TAR DNA-binding protein 43 (TDP-43) inclusion bodies can be detected in the degenerative neurons of amyotrophic lateral sclerosis. In this study, we induced chronic oxidative stress injury by applying malonate to cultured mouse cortical motor neurons. In the later stages of the malonate insult, TDP-43 expression reduced in the nuclei and transferred to the cytoplasm. This was accompanied by neuronal death, mimicking the pathological changes in TDP-43 that are seen in patients with amyotrophic lateral sclerosis. Interestingly, in the early stages of the response to malonate treatment, nuclear TDP-43 expression increased, and neurons remained relatively intact, without inclusion bodies or fragmentation. Therefore, we hypothesized that the increase of nuclear TDP-43 expression might be a pro-survival factor against oxidative stress injury. This hypothesis was confirmed by an in vitro transgenic experiment, in which overexpression of wild type mouse TDP-43 in cultured cortical motor neurons significantly reduced malonate-induced neuronal death. Our findings suggest that the loss of function of TDP-43 is an important cause of neuronal degeneration, and upregulation of nuclear TDP-43 expression might be neuroprotective in amyotrophic lateral sclerosis.

CX3CR1 is a modifying gene of survival and progression in amyotrophic lateral sclerosis

The objective of this study was to investigate the association of functional variants of the human CX3CR1 gene (Fractalkine receptor) with the risk of Amyotrophic Lateral Sclerosis (ALS), the survival and the progression rate of the disease symptoms in a Spanish ALS cohort. 187 ALS patients (142 sporadic [sALS] and 45 familial) and 378 controls were recruited. We investigated CX3CR1 V249I (rs3732379) and T280M (rs3732378) genotypes and their haplotypes as predictors of survival, the progression rate of the symptoms (as measured by ALSFRS-R and FVC decline) and the risk of suffering ALS disease. The results indicated that sALS patients with CX3CR1 249^I/I or 249^V/I genotypes presented a shorter survival time (42.27±4.90) than patients with 249^V/V genotype (67.65±7.42; diff −25.49 months 95%CI [−42.79,−8.18]; p = 0.004; adj-p = 0.018). The survival time was shorter in sALS patients with spinal topography and CX3CR1 249^I alleles (diff = −29.78 months; 95%CI [−49.42,−10.14]; p = 0.003). The same effects were also observed in the spinal sALS patients with 249^I–280^M haplotype (diff = −27.02 months; 95%CI [−49.57, −4.48]; p = 0.019). In the sALS group, the CX3CR1 249^I variant was associated with a faster progression of the disease symptoms (OR = 2.58; 95IC% [1.32, 5.07]; p = 0.006; adj-p = 0.027). There was no evidence for association of these two CX3CR1 variants with ALS disease risk. The association evidenced herein is clinically relevant and indicates that CX3CR1 could be a disease-modifying gene in sALS. The progression rate of the disease's symptoms and the survival time is affected in patients with one or two copies of the CX3CR1 249I allele. The CX3CR1 is the most potent ALS survival genetic factor reported to date. These results reinforce the role of the immune system in ALS pathogenesis.

A novel acylaminoimidazole derivative, WN1316, alleviates disease progression via suppression of glial inflammation in ALS mouse model

Amyotrophic lateral sclerosis (ALS) is an adult-onset motor neuron degenerative disease. Given that oxidative stress and resulting chronic neuronal inflammation are thought to be central pathogenic, anti-oxidative agents and modulators of neuronal inflammation could be potential therapies for ALS. We report here that the novel small molecular compound, 2-[mesityl(methyl)amino]-N-[4-(pyridin-2-yl)-1H-imidazol-2-yl] acetamide trihydrochloride (WN1316) selectively suppresses oxidative stress-induced cell death and neuronal inflammation in the late-stage ALS mice. WN1316 has high blood-brain-barrier permeability and water solubility, and boosts both neuronal apoptosis inhibitory protein (NAIP) and NF-E2-related factor 2 (Nrf2) which governed glutathione (GSH)-related anti-oxidation pathway protecting motor neurons against oxidative injuries. Post-onset oral administration of low dose (1-100 µg/kg/day) WN1316 in ALS(SOD1(H46R)) and ALS(SOD1(G93A)) mice resulted in sustained improved motor function and post onset survival rate. Immunohistochemical analysis revealed less DNA oxidative damage and motor neuronal inflammation as well as repression of both microgliosis and astrocytosis, concomitant down regulation of interleukin-1β and inducible nitric oxide synthase, and preservation of the motoneurons in anterior horn of lumbar spinal cord and skeletal muscle (quadriceps femoris). Thus, WN1316 would be a novel therapeutic agent for ALS.

The role of miRNA in motor neuron disease

microRNA is a subset of endogenous non-coding RNA. It binds to partially complementary sequences in mRNAs and inhibits mRNA translation by either blocking translational machinery or degrading mRNAs. It is involved in various cellular processes including cell cycle, development, metabolism, and synaptic plasticity. Dysregulation of miRNA expression and function is reported in various diseases including cancer, metabolic disorders as well as neurological disorders. In nervous system, miRNA related pathways play a very important role in development and function of neuronal cells. Moreover, numerous evidences suggest that dysregulated miRNA related pathways contribute to pathology of neurological disorders such as Alzheimer’s disease, amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). Here, we review current knowledge about the role of miRNAs in motor neuron disorders, especially about two common diseases: SMA and ALS.

Altered expression of atypical PKC and Ryk in the spinal cord of a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive paralysis due to the selective death of motor neurons of unknown causes. Increasing evidence indicates that Wnt signaling is altered in ALS. In this study, we focused on two non-canonical Wnt signaling components, atypical PKC (aPKC) and a Wnt receptor, Ryk, in a mouse model of ALS, SOD1 (G93A). aPKC mediates Wnt signaling to regulate growth cone guidance, axon differentiation and cell survival. Ryk is a Wnt repulsive receptor that regulates axon guidance and inhibits regeneration after spinal cord injury. aPKC expression was increased in motor neurons of the lumbar spinal cord in SOD1 (G93A) mice at both early and late stages. Interestingly, aPKC was co-localized with SOD1 in motor neuron cell bodies and extracellular aggregates, and aPKC-containing extracellular aggregates increased with disease progression. Biochemical fractionation showed that aPKC protein level was increased in the detergent-insoluble protein fraction in SOD1 (G93A) mice at late stage but decreased in the detergent-soluble fraction at symptomatic stage. These results suggest that aPKC may be sequestered in SOD1 aggregates, impairing its ability to protect motor neurons from death. Ryk expression was also increased in the motor neurons and the white matter in the ventral lumbar spinal cord of mutant SOD1 mice with a peak at early stage. These observations indicate that Wnt/aPKC and Wnt/Ryk signaling are altered in SOD1 (G93A) mice, suggesting that changed Wnt signaling may contribute to neurodegeneration in ALS.

Hereditary spastic paraplegia: clinico-pathologic features and emerging molecular mechanisms

Hereditary spastic paraplegia (HSP) is a syndrome designation describing inherited disorders in which lower extremity weakness and spasticity are the predominant symptoms. There are more than 50 genetic types of HSP. HSP affects individuals of diverse ethnic groups with prevalence estimates ranging from 1.2 to 9.6 per 100,000. Symptoms may begin at any age. Gait impairment that begins after childhood usually worsens very slowly over many years. Gait impairment that begins in infancy and early childhood may not worsen significantly. Postmortem studies consistently identify degeneration of corticospinal tract axons (maximal in the thoracic spinal cord) and degeneration of fasciculus gracilis fibers (maximal in the cervico-medullary region). HSP syndromes thus appear to involve motor-sensory axon degeneration affecting predominantly (but not exclusively) the distal ends of long central nervous system (CNS) axons. In general, proteins encoded by HSP genes have diverse functions including (1) axon transport (e.g. SPG30/KIF1A, SPG10/KIF5A and possibly SPG4/Spastin); (2) endoplasmic reticulum morphology (e.g. SPG3A/Atlastin, SPG4/Spastin, SPG12/reticulon 2, and SPG31/REEP1, all of which interact); (3) mitochondrial function (e.g. SPG13/chaperonin 60/heat-shock protein 60, SPG7/paraplegin; and mitochondrial ATP6); (4) myelin formation (e.g. SPG2/Proteolipid protein and SPG42/Connexin 47); (5) protein folding and ER-stress response (SPG6/NIPA1, SPG8/K1AA0196 (Strumpellin), SGP17/BSCL2 (Seipin), "mutilating sensory neuropathy with spastic paraplegia" owing to CcT5 mutation and presumably SPG18/ERLIN2); (6) corticospinal tract and other neurodevelopment (e.g. SPG1/L1 cell adhesion molecule and SPG22/thyroid transporter MCT8); (7) fatty acid and phospholipid metabolism (e.g. SPG28/DDHD1, SPG35/FA2H, SPG39/NTE, SPG54/DDHD2, and SPG56/CYP2U1); and (8) endosome membrane trafficking and vesicle formation (e.g. SPG47/AP4B1, SPG48/KIAA0415, SPG50/AP4M1, SPG51/AP4E, SPG52/AP4S1, and VSPG53/VPS37A). The availability of animal models (including bovine, murine, zebrafish, Drosophila, and C. elegans) for many types of HSP permits exploration of disease mechanisms and potential treatments. This review highlights emerging concepts of this large group of clinically similar disorders.

Neuroprotection by monocarbonyl dimethoxycurcumin C: ameliorating the toxicity of mutant TDP-43 via HO-1

Mutation of TAR DNA-binding protein-43 (TDP-43) was detected in familiar and sporadic amyotrophic lateral sclerosis, and pathological TDP-43 was identified in the frontotemporal lobar degeneration. The neuroprotective functions of curcumin derivatives were assessed in motor neurons transfected with mutant TDP-43. We found that curcumin derivatives reduced the levels of TDP-43 fragments. Furthermore, we evaluated these compounds on the cellular model that the cells were transfected with TDP-25. We found that the expression level and aggregate formation of TDP-25 were significantly reduced by monocarbonyl dimethoxycurcumin C (Compound C). To study on the neuroprotective functions of curcumin derivatives, the neuroblastoma-spinal cord-34 cells transfected with mutant TDP-43 were assessed by the level of lactate dehydrogenase (LDH) and malondialdehyde bisdimethyl acetal (MDA) that were involved in the oxidative stress. We found that Compound C ameliorated the damage of mutant TDP-43 by reducing the level of MDA and LDH. Furthermore, heme oxygenase-1 (HO-1) was induced by Compound C significantly higher than other compounds. Znpp, which is known an inhibitor of HO-1, dramatically interfered with the function of Compound C. In addition, Compound C was tested in vivo, and HO-1 was significantly upregulated at the hippocampus. These findings suggest that Compound C, which degrades TDP-43 fragment and strengthens the antioxidant ability by HO-1, is a promising agent for TDP-43 proteinopathy.

Emerging complexity of the HuD/ELAVl4 gene; implications for neuronal development, function, and dysfunction

Precise control of messenger RNA (mRNA) processing and abundance are increasingly being recognized as critical for proper spatiotemporal gene expression, particularly in neurons. These regulatory events are governed by a large number of trans-acting factors found in neurons, most notably RNA-binding proteins (RBPs) and micro-RNAs (miRs), which bind to specific cis-acting elements or structures within mRNAs. Through this binding mechanism, trans-acting factors, particularly RBPs, control all aspects of mRNA metabolism, ranging from altering the transcription rate to mediating mRNA degradation. In this context the best-characterized neuronal RBP, the Hu/ELAVl family member HuD, is emerging as a key component in multiple regulatory processes--including pre-mRNA processing, mRNA stability, and translation--governing the fate of a substantial amount of neuronal mRNAs. Through its ability to regulate mRNA metabolism of diverse groups of functionally similar genes, HuD plays important roles in neuronal development and function. Furthermore, compelling evidence indicates supplementary roles for HuD in neuronal plasticity, in particular, recovery from axonal injury, learning and memory, and multiple neurological diseases. The purpose of this review is to provide a detailed overview of the current knowledge surrounding the expression and roles of HuD in the nervous system. Additionally, we outline the present understanding of the molecular mechanisms presiding over the localization, abundance, and function of HuD in neurons.

Recent progress in the discovery of small molecules for the treatment of amyotrophic lateral sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder with few therapeutic options. While several gene mutations have been implicated in ALS, the exact cause of neuronal dysfunction is unknown and motor neurons of affected individuals display numerous cellular abnormalities. Ongoing efforts to develop novel ALS treatments involve the identification of small molecules targeting specific mechanisms of neuronal pathology, including glutamate excitotoxicity, mutant protein aggregation, endoplasmic reticulum (ER) stress, loss of trophic factors, oxidative stress, or neuroinflammation. Herein, we review recent advances in the discovery and preclinical characterization of lead compounds that may ultimately provide novel drugs to treat patients suffering from ALS.

Cholesterol homeostasis: a key to prevent or slow down neurodegeneration

Neurodegeneration, a common feature for many brain disorders, has severe consequences on the mental and physical health of an individual. Typically human neurodegenerative diseases are devastating illnesses that predominantly affect elderly people, progress slowly, and lead to disability and premature death; however they may occur at all ages. Despite extensive research and investments, current therapeutic interventions against these disorders treat solely the symptoms. Therefore, since the underlying mechanisms of damage to neurons are similar, in spite of etiology and background heterogeneous, it will be of interest to identify possible trigger point of neurodegeneration enabling development of drugs and/or prevention strategies that target many disorders simultaneously. Among the factors that have been identified so far to cause neurodegeneration, failures in cholesterol homeostasis are indubitably the best investigated. The aim of this review is to critically discuss some of the main results reported in the recent years in this field mainly focusing on the mechanisms that, by recovering perturbations of cholesterol homeostasis in neuronal cells, may correct clinically relevant features occurring in different neurodegenerative disorders and, in this regard, also debate the current potential therapeutic interventions.