In vitro neurotoxic properties and excitatory aminoacids concentration in the cerebrospinal fluid of amyotrophic lateral sclerosis patients. Relationship with the degree of certainty of disease diagnoses

A Review of Biomarkers of Amyotrophic Lateral Sclerosis: A Pathophysiologic Approach

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration of upper and lower motor neurons. The heterogeneous nature of ALS at the clinical, genetic, and pathological levels makes it challenging to develop diagnostic and prognostic tools that fit all disease phenotypes. Limitations associated with the functional scales and the qualitative nature of mainstay electrophysiological testing prompt the investigation of more objective quantitative assessment. Biofluid biomarkers have the potential to fill that gap by providing evidence of a disease process potentially early in the disease, its progression, and its response to therapy. In contrast to other neurodegenerative diseases, no biomarker has yet been validated in clinical use for ALS. Several fluid biomarkers have been investigated in clinical studies in ALS. Biofluid biomarkers reflect the different pathophysiological processes, from protein aggregation to muscle denervation. This review takes a pathophysiologic approach to summarizing the findings of clinical studies utilizing quantitative biofluid biomarkers in ALS, discusses the utility and shortcomings of each biomarker, and highlights the superiority of neurofilaments as biomarkers of neurodegeneration over other candidate biomarkers.

Neuronal Circuit Dysfunction in Amyotrophic Lateral Sclerosis

The primary neural circuit affected in Amyotrophic Lateral Sclerosis (ALS) patients is the corticospinal motor circuit, originating in upper motor neurons (UMNs) in the cerebral motor cortex which descend to synapse with the lower motor neurons (LMNs) in the spinal cord to ultimately innervate the skeletal muscle. Perturbation of these neural circuits and consequent loss of both UMNs and LMNs, leading to muscle wastage and impaired movement, is the key pathophysiology observed. Despite decades of research, we are still lacking in ALS disease-modifying treatments. In this review, we document the current research from patient studies, rodent models, and human stem cell models in understanding the mechanisms of corticomotor circuit dysfunction and its implication in ALS. We summarize the current knowledge about cortical UMN dysfunction and degeneration, altered excitability in LMNs, neuromuscular junction degeneration, and the non-cell autonomous role of glial cells in motor circuit dysfunction in relation to ALS. We further highlight the advances in human stem cell technology to model the complex neural circuitry and how these can aid in future studies to better understand the mechanisms of neural circuit dysfunction underpinning ALS.

Enhanced levels of fractalkine and HSP60 in cerebrospinal fluid of sporadic amyotrophic lateral sclerosis patients

Amyotrophic Lateral Sclerosis (ALS) is a multifactorial neurodegenerative disorder with a significant contribution of non-cell autonomous mechanisms to motor neuronal degeneration. Amongst a plethora of molecules, fractalkine (C-X3-C motif chemokine ligand 1), and Heat Shock Protein 60 (HSP60), are key modulators of microglial activation. The contribution of these molecules in Sporadic ALS (SALS) remains unexplored. To investigate this, fractalkine levels were estimated in Cerebrospinal fluid (CSF) of SALS patients (ALS-CSF; n = 44) by Enzyme-linked Immunosorbent Assay (ELISA) and correlated with clinical parameters including disease severity and duration. CSF HSP60 levels were estimated by Western blotting (ALS-CSF; n = 19). Also, CSF levels of Chitotriosidase-1 (CHIT-1), a microglia-specific neuroinflammatory molecule, were measured and its association, if any, with fractalkine and HSP60 was investigated. Both fractalkine and HSP60 levels were significantly elevated in ALS-CSF. Similar to our earlier observation, CHIT-1 levels were also upregulated. Fractalkine showed a moderate negative correlation with the ALS-Functional Rating Scale (ALSFRS) score indicating its significant rise in mild cases which plateaued in cases with high disease severity. However, no obvious correlation was found between fractalkine, HSP60, and CHIT-1. Our study hints that high fractalkine levels in mild cases might be conferring neuroprotection by combating microglial activation and highlights its importance as a novel therapeutic target for SALS. On the other hand, significantly enhanced levels of HSP60, a pro-inflammatory molecule, hint towards its role in accentuating microgliosis, although, it doesn't act synergistically with CHIT-1. Our study suggests that fractalkine and HSP60 act independently of CHIT-1 to suppress and accentuate neuroinflammation, respectively.

Glutamine metabolism in diseases associated with mitochondrial dysfunction

Mitochondrial dysfunction can arise from genetic defects or environmental exposures and impact a wide range of biological processes. Among these are metabolic pathways involved in glutamine catabolism, anabolism, and glutamine-glutamate cycling. In recent years, altered glutamine metabolism has been found to play important roles in the pathologic consequences of mitochondrial dysfunction. Glutamine is a pleiotropic molecule, not only providing an alternate carbon source to glucose in certain conditions, but also playing unique roles in cellular communication in neurons and astrocytes. Glutamine consumption and catabolic flux can be significantly altered in settings of genetic mitochondrial defects or exposure to mitochondrial toxins, and alterations to glutamine metabolism appears to play a particularly significant role in neurodegenerative diseases. These include primary mitochondrial diseases like Leigh syndrome (subacute necrotizing encephalopathy) and MELAS (mitochondrial myopathy with encephalopathy, lactic acidosis, and stroke-like episodes), as well as complex age-related neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Pharmacologic interventions targeting glutamine metabolizing and catabolizing pathways appear to provide some benefits in cell and animal models of these diseases, indicating glutamine metabolism may be a clinically relevant target. In this review, we discuss glutamine metabolism, mitochondrial disease, the impact of mitochondrial dysfunction on glutamine metabolic processes, glutamine in neurodegeneration, and candidate targets for therapeutic intervention.

Metabolomics as a Crucial Tool to Develop New Therapeutic Strategies for Neurodegenerative Diseases

Neurodegenerative diseases (NDs), such as Alzheimer's (AD), Parkinson's (PD), and amyotrophic lateral sclerosis (ALS), share common pathological mechanisms, including metabolism alterations. However, their specific neuronal cell types affected and molecular biomarkers suggest that there are both common and specific alterations regarding metabolite levels. In this review, we were interested in identifying metabolite alterations that have been reported in preclinical models of NDs and that have also been documented as altered in NDs patients. Such alterations could represent interesting targets for the development of targeted therapy. Importantly, the translation of such findings from preclinical to clinical studies is primordial for the study of possible therapeutic agents. We found that N-acetyl-aspartate (NAA), myo-inositol, and glutamate are commonly altered in the three NDs investigated here. We also found other metabolites commonly altered in both AD and PD. In this review, we discuss the studies reporting such alterations and the possible pathological mechanism underlying them. Finally, we discuss clinical trials that have attempted to develop treatments targeting such alterations. We conclude that the treatment combination of both common and differential alterations would increase the chances of patients having access to efficient treatments for each ND.

TDP-43 Proteinopathy Causes Broad Metabolic Alterations including TCA Cycle Intermediates and Dopamine Levels in Drosophila Models of ALS

ALS is a fatal, complex neurodegenerative disorder that causes selective degeneration of motor neurons. ALS patients exhibit symptoms consistent with altered cellular energetics such as hypermetabolism, weight loss, dyslipidemia, insulin resistance, and altered glucose tolerance. Although evidence supports metabolic changes in ALS patients, metabolic alterations at a cellular level remain poorly understood. Here, we used a Drosophila model of ALS based on TDP-43 expression in motor neurons that recapitulates hallmark features of motor neuron disease including TDP-43 aggregation, locomotor dysfunction, and reduced lifespan. To gain insights into metabolic changes caused by TDP-43, we performed global metabolomic profiling in larvae expressing TDP-43 (WT or ALS associated mutant variant, G298S) and identified significant alterations in several metabolic pathways. Here, we report alterations in multiple metabolic pathways and highlight upregulation of TCA cycle metabolites and defects in neurotransmitter levels. We also show that modulating TCA cycle flux either genetically or by dietary intervention mitigates TDP-43-dependent locomotor defects. In addition, dopamine levels are significantly reduced in the context of TDP-43G298S, and we find that treatment with pramipexole, a dopamine agonist, improves locomotor function in vivo in Drosophila models of TDP-43 proteinopathy.

40 Years of CSF Toxicity Studies in ALS: What Have We Learnt About ALS Pathophysiology?

Based on early evidence of in vitro neurotoxicity following exposure to serum derived from patients with amyotrophic lateral sclerosis (ALS), several studies have attempted to explore whether cerebrospinal fluid (CSF) obtained from people with ALS could possess similar properties. Although initial findings proved inconclusive, it is now increasingly recognized that ALS-CSF may exert toxicity both in vitro and in vivo. Nevertheless, the mechanism underlying CSF-induced neurodegeneration remains unclear. This review aims to summarize the 40-year long history of CSF toxicity studies in ALS, while discussing the various mechanisms that have been proposed, including glutamate excitotoxicity, proteotoxicity and oxidative stress. Furthermore, we consider the potential implications of a toxic CSF circulatory system in the pathophysiology of ALS, and also assess its significance in the context of current ALS research.

MR spectroscopy and imaging-derived measurements in the supplementary motor area for biomarkers of amyotrophic lateral sclerosis

The diagnosis of amyotrophic lateral sclerosis (ALS) requires both upper and lower motor neuron signs. However, quite a few patients with ALS lack the upper motor neuron sign during the disease. This study sought to investigate whether metabolites, including glutamate (Glu), N-acetyl aspartate (NAA), and gamma aminobutyric acid (GABA), in the supplementary motor area (SMA) measured by magnetic resonance spectroscopy (MRS), could be a surrogate biomarker for ALS. Twenty-five patients with ALS and 12 controls underwent 3.0-T MR scanning, which measured Glu, NAA, and GABA. Finally, receiver operating characteristic (ROC) curves were created and the area under curve (AUC) was calculated to assess the diagnostic power. Logistic regression analysis revealed the usefulness of both Glu and NAA for the differentiation of ALS from controls (Glu, P = 0.009; NAA, P = 0.033). The ratio of Glu to NAA or GABA was significantly increased in patients with ALS (Glu/NAA, P = 0.027; Glu/GABA, P = 0.003). Both the AUCs were more than 0.7, with high specificity but low sensitivity. The present findings might indicate that both the Glu/NAA and the Glu/GABA ratios in the SMA could be potential biomarkers for the diagnosis of ALS.

Defining novel functions for cerebrospinal fluid in ALS pathophysiology

Despite the considerable progress made towards understanding ALS pathophysiology, several key features of ALS remain unexplained, from its aetiology to its epidemiological aspects. The glymphatic system, which has recently been recognised as a major clearance pathway for the brain, has received considerable attention in several neurological conditions, particularly Alzheimer's disease. Its significance in ALS has, however, been little addressed. This perspective article therefore aims to assess the possibility of CSF contribution in ALS by considering various lines of evidence, including the abnormal composition of ALS-CSF, its toxicity and the evidence for impaired CSF dynamics in ALS patients. We also describe a potential role for CSF circulation in determining disease spread as well as the importance of CSF dynamics in ALS neurotherapeutics. We propose that a CSF model could potentially offer additional avenues to explore currently unexplained features of ALS, ultimately leading to new treatment options for people with ALS.

Cerebrospinal fluid cytotoxicity in amyotrophic lateral sclerosis: a systematic review of in vitro studies

Various studies have suggested that a neurotoxic cerebrospinal fluid profile could be implicated in amyotrophic lateral sclerosis. Here, we systematically review the evidence for cerebrospinal fluid cytotoxicity in amyotrophic lateral sclerosis and explore its clinical correlates. We searched the following databases with no restrictions on publication date: PubMed, Embase and Web of Science. All studies that investigated cytotoxicity in vitro following exposure to cerebrospinal fluid from amyotrophic lateral sclerosis patients were considered for inclusion. Meta-analysis could not be performed, and findings were instead narratively summarized. Twenty-eight studies were included in our analysis. Both participant characteristics and study conditions including cerebrospinal fluid concentration, exposure time and culture model varied considerably across studies. Of 22 studies assessing cell viability relative to controls, 19 studies reported a significant decrease following exposure to cerebrospinal fluid from patients with amyotrophic lateral sclerosis, while three early studies failed to observe any difference. Seven of eight studies evaluating apoptosis observed significant increases in the levels of apoptotic markers following exposure to cerebrospinal fluid from patients with amyotrophic lateral sclerosis, with the remaining study reporting a qualitative difference. Although five studies investigated the possible relationship between cerebrospinal fluid cytotoxicity and patient characteristics, such as age, gender and disease duration, none demonstrated an association with any of the factors. In conclusion, our analysis suggests that cerebrospinal fluid cytotoxicity is a feature of sporadic and possibly also of familial forms of amyotrophic lateral sclerosis. Further research is, however, required to better characterize its underlying mechanisms and to establish its possible contribution to amyotrophic lateral sclerosis pathophysiology.

P2X7 Receptor Antagonism as a Potential Therapy in Amyotrophic Lateral Sclerosis

This review focuses on the purinergic ionotropic receptor P2X7 (P2X7R) as a potential target for developing drugs that delay the onset and/or disease progression in patients with amyotrophic lateral sclerosis (ALS). Description of clinical and genetic ALS features is followed by an analysis of advantages and drawbacks of transgenic mouse models of disease based on mutations in a bunch of proteins, particularly Cu/Zn superoxide dismutase (SOD1), TAR-DNA binding protein-43 (TDP-43), Fused in Sarcoma/Translocated in Sarcoma (FUS), and Chromosome 9 open reading frame 72 (C9orf72). Though of limited value, these models are however critical to study the proof of concept of new compounds, before reaching clinical trials. The authors also provide a description of ALS pathogenesis including protein aggregation, calcium-dependent excitotoxicity, dysfunction of calcium-binding proteins, ultrastructural mitochondrial alterations, disruption of mitochondrial calcium handling, and overproduction of reactive oxygen species (ROS). Understanding disease pathogenic pathways may ease the identification of new drug targets. Subsequently, neuroinflammation linked with P2X7Rs in ALS pathogenesis is described in order to understand the rationale of placing the use of P2X7R antagonists as a new therapeutic pharmacological approach to ALS. This is the basis for the hypothesis that a P2X7R blocker could mitigate the neuroinflammatory state, indirectly leading to neuroprotection and higher motoneuron survival in ALS patients.

The RNA-binding protein FUS/TLS undergoes calcium-mediated nuclear egress during excitotoxic stress and is required for GRIA2 mRNA processing

Excitotoxic levels of glutamate represent a physiological stress that is strongly linked to amyotrophic lateral sclerosis (ALS) and other neurological disorders. Emerging evidence indicates a role for neurodegenerative disease-linked RNA-binding proteins (RBPs) in the cellular stress response. However, the relationships between excitotoxicity, RBP function, and disease have not been explored. Here, using primary cortical and motor neurons, we found that excitotoxicity induced the translocation of select ALS-linked RBPs from the nucleus to the cytoplasm within neurons. RBPs affected by excitotoxicity included TAR DNA-binding protein 43 (TDP-43) and, most robustly, fused in sarcoma/translocated in liposarcoma (FUS/TLS or FUS). We noted that FUS is translocated through a calcium-dependent mechanism and that its translocation coincides with striking alterations in nucleocytoplasmic transport. Furthermore, glutamate-induced up-regulation of glutamate ionotropic receptor α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type subunit 2 (GRIA2) in neurons depended on FUS expression, consistent with a functional role for FUS in excitotoxic stress. These findings reveal molecular links among prominent factors in neurodegenerative diseases, namely excitotoxicity, disease-associated RBPs, and nucleocytoplasmic transport.

Metabolomics Biomarkers: A Strategy Toward Therapeutics Improvement in ALS

Biomarkers research in amyotrophic lateral sclerosis (ALS) holds the promise of improving ALS diagnosis, follow-up of patients, and clinical trials outcomes. Metabolomics have a big impact on biomarkers identification. In this mini-review, we provide the main findings of metabolomics studies in ALS and discuss the most relevant therapeutics attempts that targeted some prominent alterations found in ALS, like glutamate excitotoxicity, oxidative stress, alterations in energetic metabolism, and creatinine levels. Metabolomics studies have reported putative diagnosis or prognosis biomarkers, but discrepancies among these studies did not allow validation of metabolic biomarkers for clinical use in ALS. In this context, we wonder whether metabolomics knowledge could improve ALS therapeutics. As metabolomics identify specific metabolic pathways modified by disease progression and/or treatment, we support that adjuvant or combined treatment should be used to rescue these pathways, creating a new perspective for ALS treatment. Some ongoing clinical trials are already trying to target these pathways. As clinical trials in ALS have been disappointing and considering the heterogeneity of the disease presentation, we support the application of a pharmacometabolomic approach to evaluate the individual response to drug treatments and their side effects, enabling the development of personalized treatments for ALS. We suggest that the best strategy to apply metabolomics for ALS therapeutics progress is to establish a metabolic signature for ALS patients in order to improve the knowledge of patient metabotypes, to choose the most adequate pharmacological treatment, and to follow the drug response and side effects, based on metabolomics biomarkers.

Glutamate release and uptake processes are altered in a new mouse model of amyotrophic lateral sclerosis

In this paper, we showed that in the cortex of mice expressing an abberant form of FUS protein that model amyotrophic lateral sclerosis (ALS), the processes of KCl-induced and basal [(3)H]glutamate release and uptake are altered at the presymptomatic stage as compared to the non-transgenic littermates. The change in these three parameters in transgenic animals causes excitotoxicity, which, in turn, may lead to massive loss of motor neurons and the onset of ALS symptoms.

Proteomic analysis of cerebrospinal fluid in amyotrophic lateral sclerosis

The present study used comparative proteomic analysis of cerebrospinal fluid (CSF) in amyotrophic lateral sclerosis (ALS) patients in order to identify proteins that may act as diagnostic biomarkers and indicators of the pathogenesis of ALS. This analysis was performed using isobaric tags for relative and absolute quantitation (iTRAQ) technology, coupled with 2-dimensional liquid chromatography/mass spectrometry. Database for Annotation, Visualization and Integrated Discovery software was utilized for bioinformatic analysis of the data. Following this, western blotting was performed in order to examine the expression of 3 candidate proteins in ALS patients compared with healthy individuals [as a normal control (NC) group] or patients with other neurological disease (OND); these proteins were insulin-like growth factor II (IGF-2), glutamate receptor 4 (GRIA4) and leucine-rich α-2-glycoprotein 1 (LRG1). Clinical data, including gender, age, disease duration and ALS functional rating scale (ALSFRS-R) score, were also collected in the ALS patients. Multiple linear regression analysis was performed between the clinical data and the results of western blot analysis. A total of 248 distinct proteins were identified in the ALS and NC groups, amongst which a significant difference could be identified in 35 proteins; of these, 21 proteins were downregulated and 14 were upregulated. These differentially-expressed proteins were thus revealed to be associated with ALS. The western blot analysis confirmed a proportion of the data attained in the iTRAQ analysis, revealing the differential protein expression of IGF-2 and GRIA4 between the ALS and NC groups. IGF-2 was significantly downregulated in ALS patients (P=0.017) and GRIA4 was significantly upregulated (P=0.016). These results were subsequently validated in the 35-patient ALS and OND groups (P=0.002), but no significant difference was identified in LRG1 expression between these groups. GRIA4 protein expression was higher in male than female patients and was positively correlated with the ALSFRS-R score, meaning that GRIA4 expression was negatively correlated with the severity of ALS, while IGF-2 and LRG1 expression did not correlate with any clinical data. The present study thus demonstrated that GRIA4 expression levels, as a marker of severity, may be used as a reference for the timing of treatment, and that IGF-2 may serve as an effective biomarker of ALS progression.

Cortical spreading depression-induced preconditioning in the brain

Cortical spreading depression is a technique used to depolarize neurons. During focal or global ischemia, cortical spreading depression-induced preconditioning can enhance tolerance of further injury. However, the underlying mechanism for this phenomenon remains relatively unclear. To date, numerous issues exist regarding the experimental model used to precondition the brain with cortical spreading depression, such as the administration route, concentration of potassium chloride, induction time, duration of the protection provided by the treatment, the regional distribution of the protective effect, and the types of neurons responsible for the greater tolerance. In this review, we focus on the mechanisms underlying cortical spreading depression-induced tolerance in the brain, considering excitatory neurotransmission and metabolism, nitric oxide, genomic reprogramming, inflammation, neurotropic factors, and cellular stress response. Specifically, we clarify the procedures and detailed information regarding cortical spreading depression-induced preconditioning and build a foundation for more comprehensive investigations in the field of neural regeneration and clinical application in the future.

MicroRNAs as potential circulating biomarkers for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a condition primarily characterized by the selective loss of upper and lower motor neurons. Motor neuron loss gives rise to muscle tissue malfunctions, including weakness, spasticity, atrophy, and ultimately paralysis, with death typically due to respiratory failure within 2 to 5 years of symptoms' onset. The mean delay in time from presentation to diagnosis remains at over 1 year. Biomarkers are urgently needed to facilitate ALS diagnosis and prognosis as well as to act as indicators of therapeutic response in clinical trials. MicroRNAs (miRNAs) are small molecules that can influence posttranscriptional gene expression of a variety of transcript targets. Interestingly, miRNAs can be released into the circulation by pathologically affected tissues. This review presents therapeutic and diagnostic challenges associated with ALS, highlights the potential role of miRNAs in ALS, and discusses the diagnostic potential of these molecules in identifying ALS-specific miRNAs or in distinguishing between the various genotypic and phenotypic forms of ALS.

Human cerebrospinal fluid increases the excitability of pyramidal neurons in the in vitro brain slice

KEY POINTS

The cerebrospinal fluid contains numerous neuromodulators at ambient levels but whether, and how, they affect the activity of central neurons is unknown. This study provides experimental evidence that human cerebrospinal fluid (hCSF) increases the excitability of hippocampal and neocortical pyramidal neurons. Hippocampal CA1 pyramidal neurons in hCSF displayed lowered firing thresholds, depolarized resting membrane potentials and reduced input resistance, mimicking properties of pyramidal neurons recorded in vivo. The excitability-increasing effect of hCSF on CA1 pyramidal neurons was entirely occluded by intracellular application of GTPγS, suggesting that neuromodulatory effects were mediated by G-protein coupled receptors. These results indicate that the CSF promotes spontaneous excitatory neuronal activity, and may help to explain observed differences in the activity of pyramidal neurons recorded in vivo and in vitro. The composition of brain extracellular fluid is shaped by a continuous exchange of substances between the cerebrospinal fluid (CSF) and interstitial fluid. The CSF is known to contain a wide range of endogenous neuromodulatory substances, but their collective influence on neuronal activity has been poorly investigated. We show here that replacing artificial CSF (aCSF), routinely used for perfusion of brain slices in vitro, with human CSF (hCSF) powerfully boosts spontaneous firing of CA1, CA3 and layer 5 pyramidal neurons in the rat brain slice. CA1 pyramidal neurons in hCSF display lowered firing thresholds, more depolarized resting membrane potentials and reduced input resistance, mimicking properties of pyramidal neurons recorded in vivo. The increased excitability of CA1 pyramidal neurons was completely occluded by intracellular application of GTPγS, suggesting that endogenous neuromodulators in hCSF act on G-protein coupled receptors to enhance excitability. We found no increase in spontaneous inhibitory synaptic transmission by hCSF, indicating a differential effect on glutamatergic and GABAergic neurons. Our findings highlight a previously unknown function of the CSF in promoting spontaneous excitatory activity, and may help to explain differences observed in the activity of pyramidal neurons recorded in vivo and in vitro.

Sumoylation of critical proteins in amyotrophic lateral sclerosis: emerging pathways of pathogenesis

Emerging lines of evidence suggest a relationship between amyotrophic lateral sclerosis (ALS) and protein sumoylation. Multiple studies have demonstrated that several of the proteins involved in the pathogenesis of ALS, including superoxide dismutase 1, fused in liposarcoma, and TAR DNA-binding protein 43 (TDP-43), are substrates for sumoylation. Additionally, recent studies in cellular and animal models of ALS revealed that sumoylation of these proteins impact their localization, longevity, and how they functionally perform in disease, providing novel areas for mechanistic investigations and therapeutics. In this article, we summarize the current literature examining the impact of sumoylation of critical proteins involved in ALS and discuss the potential impact for the pathogenesis of the disease. In addition, we report and discuss the implications of new evidence demonstrating that sumoylation of a fragment derived from the proteolytic cleavage of the astroglial glutamate transporter, EAAT2, plays a direct role in downregulating the expression levels of full-length EAAT2 by binding to a regulatory region of its promoter.

Regulation of nuclear TDP-43 by NR2A-containing NMDA receptors and PTEN

The dysfunction of TAR DNA-binding protein-43 (TDP-43) is implicated in neurodegenerative diseases. However, the function of TDP-43 is not fully elucidated. Here we show that the protein level of endogenous TDP-43 in the nucleus is increased in mouse cortical neurons in the early stages, but return to basal level in the later stages after glutamate accumulation-induced injury. The elevation of TDP-43 results from a downregulation of phosphatase and tensin homolog (PTEN). We further demonstrate that activation of NR2A-containing NMDA receptors (NR2ARs) leads to PTEN downregulation and subsequent reduction of PTEN import from the cytoplasm to the nucleus after glutamate accumulation. The decrease of PTEN in the nucleus contributes to its reduced association with TDP-43, and thereby mediates the elevation of nuclear TDP-43. We provide evidence that the elevation of nuclear TDP-43, mediated by NR2AR activation and PTEN downregulation, confers protection against cortical neuronal death in the late stages after glutamate accumulation. Thus, this study reveals a NR2AR-PTEN-TDP-43 signaling pathway by which nuclear TDP-43 promotes neuronal survival. These results suggest that upregulation of nuclear TDP-43 represents a self-protection mechanism to delay neurodegeneration in the early stages after glutamate accumulation and that prolonging the upregulation process of nuclear TDP-43 might have therapeutic significance.

Sporadic amyotrophic lateral sclerosis: new hypothesis regarding its etiology and pathogenesis suggests that astrocytes might be the primary target hosting a still unknown external agent

This article briefly describes the already known clinical features and pathogenic mechanisms underlying sporadic amyotrophic lateral sclerosis, namely excitoxicity, oxidative stress, protein damage, inflammation, genetic abnormalities and neuronal death. Thereafter, it puts forward the hypothesis that astrocytes may be the cells which serve as targets for the harmful action of a still unknown environmental agent, while neuronal death may be a secondary event following the initial insult to glial cells. The article also suggests that an emergent virus or a misfolded infectious protein might be potential candidates to accomplish this task.

CSF from amyotrophic lateral sclerosis patients produces glutamate independent death of rat motor brain cortical neurons: protection by resveratrol but not riluzole

The neurotoxic effects of cerebrospinal fluid (CSF) from patients suffering amyotrophic lateral sclerosis (ALS), have been reported by various authors. However, variable results have been communicated and the mechanism of such neurotoxicity has been attributed to excess glutamate concentrations in ALS/CSF. We have studied here the properties of 14 CSFs from control patients and 29 CSFs from patients of ALS. We found that while ALS/CSF impairs the viability of rat brain cortical motoneurons maintained in primary cultures, this effect seemed to be exerted through a glutamate-independent mechanism. Resveratrol protected against such neurotoxic effects and antagonized the [Ca(+2)](c) elevation produced by ALS/CSF. However, riluzole did not afford protection and antagonized the resveratrol-elicited neuroprotective effects. We conclude that ALS/CSF elicited neurotoxicity on in vitro cultures of rat brain cortical motor neurons may become a sound microassay to test available novel multitargeted neuroprotective compounds with potential therapeutic application in ALS patients.

Abnormal exocytotic release of glutamate in a mouse model of amyotrophic lateral sclerosis

Glutamate-mediated excitotoxicity plays a major role in the degeneration of motor neurons in amyotrophic lateral sclerosis and reduced astrocytary glutamate transport, which in turn increases the synaptic availability of the amino acid neurotransmitter, was suggested as a cause. Alternatively, here we report our studies on the exocytotic release of glutamate as a possible source of excessive glutamate transmission. The basal glutamate efflux from spinal cord nerve terminals of mice-expressing human soluble superoxide dismutase (SOD1) with the G93A mutation [SOD1/G93A(+)], a transgenic model of amyotrophic lateral sclerosis, was elevated when compared with transgenic mice expressing the wild-type human SOD1 or to non-transgenic controls. Exposure to 15 mM KCl or 0.3 μM ionomycin provoked Ca(2+)-dependent glutamate release that was dramatically increased in late symptomatic and in pre-symptomatic SOD1/G93A(+) mice. Increased Ca(2+) levels were detected in SOD1/G93A(+) mouse spinal cord nerve terminals, accompanied by increased activation of Ca(2+)/calmodulin-dependent kinase II and increased phosphorylation of synapsin I. In line with these findings, release experiments suggested that the glutamate release augmentation involves the readily releasable pool of vesicles and a greater capability of these vesicles to fuse upon stimulation in SOD1/G93A(+) mice.

Endogenous progesterone is associated to amyotrophic lateral sclerosis prognostic factors

Negative prognostic factors in amyotrophic lateral sclerosis include advanced age, shorter time from disease onset to diagnosis, bulbar onset and rapid progression rate.

OBJECTIVE

To compare progesterone (PROG) and cortisol serum levels in patients and controls and ascertain its relationship to prognostic factors and survival.

METHODS

We assessed serum hormonal levels in 27 patients and 21 controls.

RESULTS

Both hormones were 1.4-fold higher in patients. PROG showed a negative correlation with age, positive correlation with survival and positive trend with time to diagnosis. Increased PROG was observed in spinal onset and slow progression patients. No correlation was demonstrated with cortisol.

CONCLUSION

Increased hormonal levels in patients are probably due to hypothalamic-pituitary-adrenal axis activation. Nevertheless, in this preliminary report only PROG correlated positively with factors predicting better prognosis and survival. We hypothesize endogenous PROG and cortisol may be engaged in differential roles, the former possibly involved in a neuroprotective response.

1H-NMR-based metabolomic profiling of CSF in early amyotrophic lateral sclerosis

Background

Pathophysiological mechanisms involved in amyotrophic lateral sclerosis (ALS) are complex and none has identified reliable markers useful in routine patient evaluation. The aim of this study was to analyze the CSF of patients with ALS by ¹H NMR (Nuclear Magnetic Resonance) spectroscopy in order to identify biomarkers in the early stages of the disease, and to evaluate the biochemical factors involved in ALS.

Methodology

CSF samples were collected from patients with ALS at the time of diagnosis and from patients without neurodegenerative diseases. One and two-dimensional ¹H NMR analyses were performed and metabolites were quantified by the ERETIC method. We compared the concentrations of CSF metabolites between both groups. Finally, we performed principal component (PCA) and discriminant analyses.

Principal Findings

Fifty CSF samples from ALS patients and 44 from controls were analyzed. We quantified 17 metabolites including amino-acids, organic acids, and ketone bodies. Quantitative analysis revealed significantly lower acetate concentrations (p = 0.0002) in ALS patients compared to controls. Concentration of acetone trended higher (p = 0.015), and those of pyruvate (p = 0.002) and ascorbate (p = 0.003) were higher in the ALS group. PCA demonstrated that the pattern of analyzed metabolites discriminated between groups. Discriminant analysis using an algorithm of 17 metabolites revealed that patients were accurately classified 81.6% of the time.

Conclusion/Significance

CSF screening by NMR spectroscopy could be a useful, simple and low cost tool to improve the early diagnosis of ALS. The results indicate a perturbation of glucose metabolism, and the need to further explore cerebral energetic metabolism.