Advanced Glycation Endproducts in Neurofilament Conglomeration of Motoneurons in Familial and Sporadic Amyotrophic Lateral Sclerosis

Molecular mechanisms of neurofilament alterations and its application in assessing neurodegenerative disorders

Neurofilaments are intermediate filaments present in neurons. These provide structural support and maintain the size and shape of the neurons. Dysregulation, mutation, and aggregation of neurofilaments raise the levels of these proteins in the blood and cerebrospinal fluid (CSF), which are characteristic features of axonal damage and certain rare neurological diseases, such as Giant Axonal Neuropathy and Charcot-Mare-Tooth disease. Understanding the structure, dynamics, and function of neurofilaments has been greatly enhanced by a diverse range of biochemical and preclinical investigations conducted over more than four decades. Recently, there has been a resurgence of interest in post-translational modifications of neurofilaments, such as phosphorylation, aggregation, mutation, oxidation, etc. Over the past twenty years, several rare disorders have been studied from structural alterations of neurofilaments. These disorders are monitored by fluid biomarkers such as neurofilament light chains. Currently, there are many tools, such as Enzyme-Linked Immunosorbent Assay, Electrochemiluminescence Assay, Single-Molecule Array, Western/immunoblotting, etc., in use to assess the neurofilament proteins in Blood and CSF. However, all these techniques utilize expensive, non-specific, or antibody-based methods, which make them unsuitable for routine screening of neurodegenerative disorders. This provides room to search for newer sensitive, cost-effective, point-of-care tools for rapid screening of the disease. For a long time, the molecular mechanisms of neurofilaments have been poorly understood due to insufficient research attempts, and a deeper understanding of them remains elusive. Therefore, this review aims to highlight the available literature on molecular mechanisms of neurofilaments and the function of neurofilaments in axonal transport, axonal conduction, axonal growth, and neurofilament aggregation, respectively. Further, this review discusses the role of neurofilaments as potential biomarkers for the identification of several neurodegenerative diseases in clinical laboratory practice.

Receptors for Advanced Glycation End Products (RAGE): Promising Targets Aiming at the Treatment of Neurodegenerative Conditions

Advanced glycation end products (AGEs) are compounds formed after the non-enzymatic addition of reducing sugars to lipids, proteins, and nucleic acids. They are associated with the development of various clinical complications observed in diabetes and cardiovascular diseases, such as retinopathy, nephropathy, diabetic neuropathy, and others. In addition, compelling evidence indicates that these molecules participate in the progression of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Multiple cellular and molecular alterations triggered by AGEs that could alter homeostasis have been identified. One of the main targets for AGE signaling is the receptor for advanced glycation end-products (RAGE). Importantly, this receptor is the target of not only AGEs, but also amyloid β peptides, HMGB1 (high-mobility group box-1), members of the S100 protein family, and glycosaminoglycans. The activation of this receptor induces intracellular signaling cascades that are involved in pathological processes and cell death. Therefore, RAGE represents a key target for pharmacological interventions in neurodegenerative diseases. This review will discuss the various effects of AGEs and RAGE activation in the pathophysiology of neurodegenerative diseases, as well as the currently available pharmacological tools and promising drug candidates.

The 2022 Lady Estelle Wolfson lectureship on neurofilaments

Neurofilament proteins (Nf) have been validated and established as a reliable body fluid biomarker for neurodegenerative pathology. This review covers seven Nf isoforms, Nf light (NfL), two splicing variants of Nf medium (NfM), two splicing variants of Nf heavy (NfH),α -internexin (INA) and peripherin (PRPH). The genetic and epigenetic aspects of Nf are discussed as relevant for neurodegenerative diseases and oncology. The comprehensive list of mutations for all Nf isoforms covers Amyotrophic Lateral Sclerosis, Charcot-Marie Tooth disease, Spinal muscular atrophy, Parkinson Disease and Lewy Body Dementia. Next, emphasis is given to the expanding field of post-translational modifications (PTM) of the Nf amino acid residues. Protein structural aspects are reviewed alongside PTMs causing neurodegenerative pathology and human autoimmunity. Molecular visualisations of NF PTMs, assembly and stoichiometry make use of Alphafold2 modelling. The implications for Nf function on the cellular level and axonal transport are discussed. Neurofilament aggregate formation and proteolytic breakdown are reviewed as relevant for biomarker tests and disease. Likewise, Nf stoichiometry is reviewed with regard to in vitro experiments and as a compensatory mechanism in neurodegeneration. The review of Nf across a spectrum of 87 diseases from all parts of medicine is followed by a critical appraisal of 33 meta-analyses on Nf body fluid levels. The review concludes with considerations for clinical trial design and an outlook for future research.

Advanced Glycation End Products in Health and Disease

Advanced glycation end products (AGEs), formed through the nonenzymatic reaction of reducing sugars with the side-chain amino groups of lysine or arginine of proteins, followed by further glycoxidation reactions under oxidative stress conditions, are involved in the onset and exacerbation of a variety of diseases, including diabetes, atherosclerosis, and Alzheimer’s disease (AD) as well as in the secondary stages of traumatic brain injury (TBI). AGEs, in the form of intra- and interprotein crosslinks, deactivate various enzymes, exacerbating disease progression. The interactions of AGEs with the receptors for the AGEs (RAGE) also result in further downstream inflammatory cascade events. The overexpression of RAGE and the AGE-RAGE interactions are especially involved in cases of Alzheimer’s disease and other neurodegenerative diseases, including TBI and amyotrophic lateral sclerosis (ALS). Maillard reactions are also observed in the gut bacterial species. The protein aggregates found in the bacterial species resemble those of AD and Parkinson’s disease (PD), and AGE inhibitors increase the life span of the bacteria. Dietary AGEs alter the gut microbiota composition and elevate plasma glycosylation, thereby leading to systemic proinflammatory effects and endothelial dysfunction. There is emerging interest in developing AGE inhibitor and AGE breaker compounds to treat AGE-mediated pathologies, including diabetes and neurodegenerative diseases. Gut-microbiota-derived enzymes may also function as AGE-breaker biocatalysts. Thus, AGEs have a prominent role in the pathogenesis of various diseases, and the AGE inhibitor and AGE breaker approach may lead to novel therapeutic candidates.

Understanding the Role of Protein Glycation in the Amyloid Aggregation Process

Protein function and flexibility is directly related to the native distribution of its structural elements and any alteration in protein architecture leads to several abnormalities and accumulation of misfolded proteins. This phenomenon is associated with a range of increasingly common human disorders, including Alzheimer and Parkinson diseases, type II diabetes, and a number of systemic amyloidosis characterized by the accumulation of amyloid aggregates both in the extracellular space of tissues and as intracellular deposits. Post-translational modifications are known to have an active role in the in vivo amyloid aggregation as able to affect protein structure and dynamics. Among them, a key role seems to be played by non-enzymatic glycation, the most unwanted irreversible modification of the protein structure, which strongly affects long-living proteins throughout the body. This study provided an overview of the molecular effects induced by glycation on the amyloid aggregation process of several protein models associated with misfolding diseases. In particular, we analyzed the role of glycation on protein folding, kinetics of amyloid formation, and amyloid cytotoxicity in order to shed light on the role of this post-translational modification in the in vivo amyloid aggregation process.

Neurofilaments: neurobiological foundations for biomarker applications

Interest in neurofilaments has risen sharply in recent years with recognition of their potential as biomarkers of brain injury or neurodegeneration in CSF and blood. This is in the context of a growing appreciation for the complexity of the neurobiology of neurofilaments, new recognition of specialized roles for neurofilaments in synapses and a developing understanding of mechanisms responsible for their turnover. Here we will review the neurobiology of neurofilament proteins, describing current understanding of their structure and function, including recently discovered evidence for their roles in synapses. We will explore emerging understanding of the mechanisms of neurofilament degradation and clearance and review new methods for future elucidation of the kinetics of their turnover in humans. Primary roles of neurofilaments in the pathogenesis of human diseases will be described. With this background, we then will review critically evidence supporting use of neurofilament concentration measures as biomarkers of neuronal injury or degeneration. Finally, we will reflect on major challenges for studies of the neurobiology of intermediate filaments with specific attention to identifying what needs to be learned for more precise use and confident interpretation of neurofilament measures as biomarkers of neurodegeneration.

GlyStruct: glycation prediction using structural properties of amino acid residues

Background

Glycation is a one of the post-translational modifications (PTM) where sugar molecules and residues in protein sequences are covalently bonded. It has become one of the clinically important PTM in recent times attributed to many chronic and age related complications. Being a non-enzymatic reaction, it is a great challenge when it comes to its prediction due to the lack of significant bias in the sequence motifs.

Results

We developed a classifier, GlyStruct based on support vector machine, to predict glycated and non-glycated lysine residues using structural properties of amino acid residues. The features used were secondary structure, accessible surface area and the local backbone torsion angles. For this work, a benchmark dataset was extracted containing 235 glycated and 303 non-glycated lysine residues. GlyStruct demonstrated improved performance of approximately 10% in comparison to benchmark method of Gly-PseAAC. The performance for GlyStruct on the metrics, sensitivity, specificity, accuracy and Mathew’s correlation coefficient were 0.7013, 0.7989, 0.7562, and 0.5065, respectively for 10-fold cross-validation.

Conclusion

Glycation has emerged to be one of the clinically important PTM of proteins in recent times. Therefore, the development of computational tools become necessary to predict glycation, which could help medical professionals administer drugs and manage patients more effectively. The proposed predictor manages to classify glycated and non-glycated lysine residues with promising results consistently on various cross-validation schemes and outperforms other state of the art methods.

Electronic supplementary material

The online version of this article (10.1186/s12859-018-2547-x) contains supplementary material, which is available to authorized users.

Impact of Non-Enzymatic Glycation in Neurodegenerative Diseases: Role of Natural Products in Prevention

Non-enzymatic protein glycosylation is the addition of free carbonyls to the free amino groups of proteins, amino acids, lipoproteins and nucleic acids resulting in the formation of early glycation products. The early glycation products are also known as Maillard reaction which undergoes dehydration, cyclization and rearrangement to form advanced glycation end-products (AGEs). By and large the researchers in the past have also established that glycation and the AGEs are responsible for most type of metabolic disorders, including diabetes mellitus, cancer, neurological disorders and aging. The amassing of AGEs in the tissues of neurodegenerative diseases shows its involvement in diseases. Therefore, it is likely that inhibition of glycation reaction may extend the lifespan of an individual. The hunt for inhibitors of glycation, mainly using in vitro models, has identified natural compounds able to prevent glycation, especially polyphenols and other natural antioxidants. Extrapolation of results of in vitro studies on the in vivo situation is not straightforward due to differences in the conditions and mechanism of glycation, and bioavailability problems. Nevertheless, existing data allow postulating that enrichment of diet in natural anti-glycating agents may attenuate glycation and, in consequence may halt the aging and neurological problems.

Nitration and Glycation Turn Mature NGF into a Toxic Factor for Motor Neurons: A Role for p75NTR and RAGE Signaling in ALS

INTRODUCTION

Glycating stress can occur together with oxidative stress during neurodegeneration and contribute to the pathogenic mechanism. Nerve growth factor (NGF) accumulates in several neurodegenerative diseases. Besides promoting survival, NGF can paradoxically induce cell death by signaling through the p75 neurotrophin receptor (p75^NTR). The ability of NGF to induce cell death is increased by nitration of its tyrosine residues under conditions associated with increased peroxynitrite formation.

AIMS

Here we investigated whether glycation also changes the ability of NGF to induce cell death and assessed the ability of post-translational modified NGF to signal through the receptor for advanced glycation end products (RAGEs). We also explored the potential role of RAGE-p75^NTR interaction in the motor neuron death occurring in amyotrophic lateral sclerosis (ALS) models.

RESULTS

Glycation promoted NGF oligomerization and ultimately allowed the modified neurotrophin to signal through RAGE and p75^NTR to induce motor neuron death at low physiological concentrations. A similar mechanism was observed for nitrated NGF. We provide evidence for the interaction of RAGE with p75^NTR at the cell surface. Moreover, we observed that post-translational modified NGF was present in the spinal cord of an ALS mouse model. In addition, NGF signaling through RAGE and p75^NTR was involved in astrocyte-mediated motor neuron toxicity, a pathogenic feature of ALS.

INNOVATION

Oxidative modifications occurring under stress conditions can enhance the ability of mature NGF to induce neuronal death at physiologically relevant concentrations, and RAGE is a new p75^NTR coreceptor contributing to this pathway.

CONCLUSION

Our results indicate that NGF-RAGE/p75^NTR signaling may be a therapeutic target in ALS. Antioxid. Redox Signal. 28, 1587-1602.

Upregulation of Vesicular Glutamate Transporter 2 and STAT3 Activation in the Spinal Cord of Mice Receiving 3,3'-Iminodipropionitrile

Chronic administration of 3,3'-iminodipropionitrile (IDPN) causes axonal impairment. Although controversy still remains, it has been suggested that IDPN intoxication mimics the axonopathy of amyotrophic lateral sclerosis (ALS). Interestingly, recent studies including our own showed that signal transducer and activator of transcription 3 (STAT3) in spinal α-motoneurons was activated in both IDPN-treated mice and SOD1 ^G93A mice, a genetic model of familial ALS. Because activation of STAT3 occurs in response to various stimuli, such as axonal injury, ischemia, and excessive glutamate, here we focused on a potential link between phosphorylated STAT3 (pSTAT3, an active form) and vesicular glutamate transporter 2 (VGluT2, a regulator of glutamate storage and release) in IDPN-treated mice and SOD1 ^G93A mice. Impairment of axonal transport was confirmed by western blot analysis: the expression levels of phosphorylated neurofilament H were elevated in both models. As shown in SOD1 ^G93A mice, the expression frequencies of VGluT2 in synaptophysin-positive (SYP)⁺ presynaptic terminals around spinal α-motoneurons were significantly higher in IDPN-treated mice than in vehicle controls. The coverages of spinal α-motoneurons by VGluT2⁺ presynaptic terminals were more elevated around pSTAT3⁺ cells than around pSTAT3^- cells in IDPN-treated mice and SOD1 ^G93A mice. Considering that excessive glutamate is shown to be involved in axonal impairment and STAT3 activation, the present results suggest that IDPN-induced upregulation of VGluT2 may result in an increase in glutamate, which might cause axonopathy and induction of pSTAT3. The link between upregulation of VGluT2 and activation of STAT3 via glutamate may represent a common pathological feature of IDPN-treated mice and SOD1 ^G93A mice.

Glycation in Demetalated Superoxide Dismutase 1 Prevents Amyloid Aggregation and Produces Cytotoxic Ages Adducts

Superoxide dismutase 1 (SOD1) has been implicated with familial amyotrophic lateral sclerosis (fALS) through accumulation of protein amyloid aggregates in motor neurons of patients. Amyloid aggregates and protein inclusions are a common pathological feature of many neurological disorders in which protein aggregation seems to be directly related to neurotoxicity. Although, extensive studies performed on the aggregation process of several amyloidogenic proteins in vitro allowed the identification of many physiological factors involved, the molecular mechanisms underlying the formation of amyloid aggregates in vivo and in pathological conditions are still poorly understood. Post-translational modifications are known to affect protein structure and function and, recently, much attention has been devoted to the role played by non-enzymatic glycation in stimulating amyloid aggregation and cellular toxicity. In particular, glycation seems to have a determining role both in sporadic and familial forms of ALS and SOD1 has been shown to be glycated in vivo The aim of this study was to investigate the role of glycation on the amyloid aggregation process of both wild-type SOD1 and its ALS-related mutant G93A. To this aim, the glycation kinetics of both native and demetalated SOD have been followed using two different glycating agents, i.e., D-ribose and methylglyoxal. The effect of glycation on the structure and the amyloid aggregation propensity of native and ApoSOD has been also investigated using a combination of biophysical and biochemical techniques. In addition, the effect of SOD glycated species on cellular toxicity and reactive oxygen species (ROS) production has been evaluated in different cellular models. The results provided by this study contribute to clarify the role of glycation in amyloid aggregation and suggest a direct implication of glycation in the pathology of fALS.

Receptor for advanced glycation end-products in neurodegenerative diseases

This review, for the first time, aims to summarize the current knowledge in the emerging field of RAGE (receptor for advanced glycation end-products) studies in neurodegeneration and neurodegenerative diseases. RAGE, a member of the multiligand cell surface immunoglobulin family, has been implicated in numerous pathological conditions - from diabetes and cardiovascular diseases to tumors and neurodegenerative disorders, such as Alzheimer's disease, familial amyloid polyneuropathy, diabetic neuropathy, Parkinson's disease, and Huntington's disease. Until now, the detailed mechanisms of the contribution of RAGE to neurodegeneration remain elusive; however, mounting evidence suggests that its detrimental actions are triggered by its ligand interactions and contribute to increased neuroinflammation, neuronal degeneration, and apoptosis. Deciphering the role of RAGE in neurodegenerative disorders will be a milestone in our basic understanding of the mechanisms involved in the pathogenesis of neurodegeneration, helping to delineate molecular links between complex RAGE signaling pathways and neuronal dysfunction and neurodegeneration.

RAGE axis in neuroinflammation, neurodegeneration and its emerging role in the pathogenesis of amyotrophic lateral sclerosis

RAGE, the receptor of advanced glycation end-products, is thought to be one of the potential contributors to the neurodegeneration. It has been shown that RAGE activation triggers an increase in proinflammatory molecules, oxidative stressors and cytokines. RAGE involvement has been documented in the pathogenesis of a number of neurodegenerative diseases such amyotrophic lateral sclerosis (ALS), Alzheimer's, Parkinson's, Huntington's, Creutzfeld-Jakob' diseases and various neurodegenerative conditions such as diabetic neuropathy, familial amyloid polyneuropathy, Charcot neuroarthropathy and vasculitic neuropathy. Although the detailed mechanisms of RAGE contribution to the neurodegeneration remains unclear, studies indicate that RAGE detrimental actions are exerted via its binding to the pro-inflammatory ligands such as advanced glycation end-products, S100/calgranulin and amphoterin and subsequent activation of downstream regulatory pathways such as NF-κB, STAT and JKN pathways. Here, in this review we attempt to shed light onto molecular events and pathological pathways involved in neuroinflammation, neurodegeneration and its emerging role in the pathogenesis of amyotrophic lateral sclerosis (ALS)--a progressive and fatal neurodegenerative disorder, summarizing current knowledge and the prospect of RAGE in the pathogenesis of this disastrous disease.

The role of advanced glycation end products in various types of neurodegenerative disease: a therapeutic approach

Protein glycation is initiated by a nucleophilic addition reaction between the free amino group from a protein, lipid or nucleic acid and the carbonyl group of a reducing sugar. This reaction forms a reversible Schiff base, which rearranges over a period of days to produce ketoamine or Amadori products. The Amadori products undergo dehydration and rearrangements and develop a cross-link between adjacent proteins, giving rise to protein aggregation or advanced glycation end products (AGEs). A number of studies have shown that glycation induces the formation of the β-sheet structure in β-amyloid protein, α-synuclein, transthyretin (TTR), copper-zinc superoxide dismutase 1 (Cu, Zn-SOD-1), and prion protein. Aggregation of the β-sheet structure in each case creates fibrillar structures, respectively causing Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, familial amyloid polyneuropathy, and prion disease. It has been suggested that oligomeric species of glycated α-synuclein and prion are more toxic than fibrils. This review focuses on the pathway of AGE formation, the synthesis of different types of AGE, and the molecular mechanisms by which glycation causes various types of neurodegenerative disease. It discusses several new therapeutic approaches that have been applied to treat these devastating disorders, including the use of various synthetic and naturally occurring inhibitors. Modulation of the AGE-RAGE axis is now considered promising in the prevention of neurodegenerative diseases. Additionally, the review covers several defense enzymes and proteins in the human body that are important anti-glycating systems acting to prevent the development of neurodegenerative diseases.

Role of platelet derived growth factor (PDGF) in reverting neuronal nuclear and soma size alterations in NSC-34 cells exposed to cerebrospinal fluid from amyotrophic lateral sclerosis patients

PURPOSE

Amyotrophic lateral sclerosis (ALS) or motor neuron disease is an adult-onset progressive neurodegenerative disorder. ALS-CSF has been shown to produce toxic effects on motor neuron cells like aberrant neurofilament phosphorylation and morphological alterations of nuclear and soma size. Our current study was designed to investigate the neuroprotective role of platelet derived growth factor (PDGF) in reverting the adverse effects produced by ALS-CSF.

METHODS

Our present study was carried out to determine the restorative potential of PDGF on the toxic effects of ALS-CSF on NSC motor neuron cells from patients. Therefore the cells were divided in to three groups: (a) normal control (NC) - the cells were not exposed to ALS-CSF; (b) ALS group - the cells were exposed to ALS-CSF; (c) NALS group - the cells were exposed to non ALS CSF. Further each of these groups was supplemented with PDGF.

RESULTS AND CONCLUSIONS

We observed that the mean area of nucleus and cell soma of the differentiated NSC motor neuron cells was significantly reduced in the cells exposed to ALS-CSF. We also observed that subsequent treatment with PDGF restored the soma area and nucleus of the ALS-CSF exposed cells significantly. Taken together, we show that supplementation with PDGF restores the morphological changes induced by ALS-CSF and PDGF may play a significant role in protecting motor neurons from apoptosis in ALS and thereby it promoting the cell survival.

Glycated proteome: from reaction to intervention

Glycation, a nonenzymatic reaction between reducing sugars and proteins, is a proteome wide phenomenon, predominantly observed in diabetes due to hyperglycemia. Glycated proteome of plasma, kidney, lens, and brain are implicated in the pathogenesis of various diseases, including diabetic complications, neurodegenerative diseases, cancer, and aging. This review discusses the strategies to characterize protein glycation, its functional implications in different diseases, and intervention strategies to protect the deleterious effects of protein glycation.

Characterization of the glycated human cerebrospinal fluid proteome

Protein glycation is a nonenzymatic modification that involves pathological functions in neurological diseases. Despite the high number of studies showing accumulation of advanced end glycation products (AGEs) at clinical stage, there is a lack of knowledge about which proteins are modified, where those modifications occur, and to what extent. The goal of this study was to achieve a comprehensive characterization of proteins modified by early glycation in human cerebrospinal fluid (CSF). Approaches based on glucose diferential labeling and mass spectrometry have been applied to evaluate the glycated CSF proteome at two physiological conditions: native glucose level and in vitro high glucose content. For both purposes, detection of glycated proteins was carried out by HCD-MS2 and CID-MS3 modes after endoproteinase Glu-C digestion and boronate affinity chromatography. The abundance of glycation was assessed by protein labeling with (13)C(6)-glucose incubation. The analysis of native glycated CSF identified 111 glycation sites corresponding to 48 glycated proteins. Additionally, the in vitro high glucose level approach detected 265 glycation sites and 101 glycated proteins. The comparison of glycation levels under native and 15 mM glucose conditions showed relative concentration increases up to ten folds for some glycated proteins. This report revealed for the first time a number of key glycated CSF proteins known to be involved in neuroinflammation and neurodegenerative disorders. Altogether, the present study contains valuable and unique information, which should further help to clarify the pathological role of glycation in central nervous system pathologies. This article is part of a Special Issue entitled: Translational Proteomics.

Advanced glycation end products overload might explain intracellular cobalamin deficiency in renal dysfunction, diabetes and aging

Advanced glycation end products (AGEs) contribute to aging. Cobalamin (Cbl) is required for cell growth and functions, and its deficiency causes serious complications. Diabetics and renal patients show high concentrations of Cbl, but metabolic evidence of Cbl deficiency that is reversible after Cbl treatment. Cbl might be sequestered in blood and cannot be delivered to the cell. Megalin mediates the uptake of transcobalamin-Cbl complex into the proximal tubule cells. Megalin is involved in the uptake and degradation of AGEs. In aging, diabetes or renal dysfunction, AGEs might overload megalin thus lowering Cbl uptake. Transcobalamin-Cbl might retain in blood. Shedding of megalin and transcobalamin receptor under glycation conditions is also a possible mechanism of this phenomenon.

Neuronal intermediate filaments and neurodegenerative disorders

Intermediate filaments represent the most abundant cytoskeletal element in mature neurons. Mutations and/or accumulations of neuronal intermediate filament proteins are frequently observed in several human neurodegenerative disorders. Although it is now admitted that disorganization of the neurofilament network may be directly involved in neurodegeneration, certain type of perikaryal intermediate filament aggregates confer protection in motor neuron disease. The use of various mouse models provided a better knowledge of the role played by the disorganization of intermediate filaments in the pathogenesis of neurodegenerative disorders, but the mechanisms leading to the formation of these aggregates remain elusive. Here, we will review some neurodegenerative diseases involving intermediate filaments abnormalities and possible mechanisms susceptible to provoke them.

Amyotrophic lateral sclerosis: from current developments in the laboratory to clinical implications

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive degeneration of motor neurons occurring both as a sporadic and a familial disease. The etiology of ALS remains unknown, but one fifth of instances are due to specific gene defects, the best characterized of which is point mutations in the gene coding for Cu/Zn superoxide dismutase (SOD1). Because sporadic and familial ALS affect the same neurons with similar pathology, it is hoped that understanding these gene defects will help in devising therapies effective in both forms. A wealth of evidence has been collected in rodents made transgenic for mutant SOD1, which represent the best available models for familial ALS. Mutant SOD1 likely induces selective vulnerability of motor neurons through a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, cytoskeletal abnormalities and defective axonal transport, excitotoxicity, inadequate growth factor signaling, and inflammation. Damage within motor neurons is enhanced by noxious signals originating from nonneuronal neighboring cells, where mutant SOD1 induces an inflammatory response that accelerates disease progression. The clinical implication of these findings is that promising therapeutic approaches can be derived from multidrug treatments aimed at the simultaneous interception of damage in both motor neurons and nonmotor neuronal cells.

Advanced glycation and lipoxidation end products--amplifiers of inflammation: the role of food

BACKGROUND

High levels of glycated and lipoxidated proteins and peptides in the body are repeatedly associated with chronic diseases. These molecules are strongly associated with activation of a specific receptor called RAGE and a long-lasting exaggerated level of inflammation in the body.

METHODS

PubMed reports over 5000 papers plus >13,500 articles about the related HbA(1c), most of them published in the past 5 years. Most of the available abstracts have been read and approximately 800 full papers have been studied.

RESULTS

RAGE, a member of the immunoglobulin superfamily of cell surface molecules and receptor for advanced glycation end products, known since 1992, functions as a master switch, induces sustained activation of nuclear factor kappaB (NFkappaB), suppresses a series of endogenous autoregulatory functions, and converts long-lasting proinflammatory signals into sustained cellular dysfunction and disease. Its activation is associated with high levels of dysfunctioning proteins in body fluids and tissues, and is strongly associated with a series of diseases from allergy and Alzheimers to rheumatoid arthritis and urogenital disorders. Heat treatment, irradiation, and ionization of foods increase the content of dysfunctioning molecules.

CONCLUSIONS

More than half of the studies are performed in diabetes and chronic renal diseases; there are few studies in other diseases. Most of our knowledge is based on animal studies and in vitro studies. These effects are worth further exploration both experimentally and clinically. An avoidance of foods rich in deranged proteins and peptides, and the consumption of antioxidants, especially polyphenols, seem to counteract such a development.

Glyoxalase I A111E, paraoxonase 1 Q192R and L55M polymorphisms: susceptibility factors of multiple sclerosis?

Multiple sclerosis (MS) is characterized by chronic inflammation and demyelination of the central nervous system (CNS). Accumulating data indicate that oxidative stress, leading to reactive oxygen species (ROS) production and lipid peroxidation, as well as elevated levels of advanced glycation end products (AGE) in CNS neurons, might play a pivotal role in the pathogenesis of a number of diseases with a neurodegenerative aspect, such as MS. Therefore, polymorphisms of genes encoding endogenous free-radical scavenging systems, such as paraoxonase 1 (PON1), and anti-glycation defences, such as glyoxalase I (GI), could influence susceptibility to MS. In the present study, we have undertaken a case-control study to investigate the possible association of GI A111E, PON1 Q192R and L55M polymorphisms with the risk of MS. The three polymorphisms were characterized in 209 patients with relapsing-remitting MS (RRMS) and in 213 healthy controls by PCR/RFLP methods using DNA from lymphocytes. We found that individuals with the GI/AE-EE genotypes and PON55/LM-MM genotypes had a significantly higher risk of MS compared with the other genotypes. The two polymorphisms appear to be common genetic traits that are associated with an increased risk for MS--the analysis of both, in each single case, may be a revealing predictable factor for MS risk.

Redox proteomics in some age-related neurodegenerative disorders or models thereof

Neurodegenerative diseases cause memory loss and cognitive impairment. Results from basic and clinical scientific research suggest a complex network of mechanisms involved in the process of neurodegeneration. Progress in treatment of such disorders requires researchers to better understand the functions of proteins involved in neurodegenerative diseases, to characterize their role in pathogenic disease mechanisms, and to explore their roles in the diagnosis, treatment, and prevention of neurodegenerative diseases. A variety of conditions of neurodegenerative diseases often lead to post-translational modifications of proteins, including oxidation and nitration, which might be involved in the pathogenesis of neurodegenerative diseases. Redox proteomics, a subset of proteomics, has made possible the identification of specifically oxidized proteins in neurodegenerative disorders, providing insight into a multitude of pathways that govern behavior and cognition and the response of the nervous system to injury and disease. Proteomic analyses are particularly suitable to elucidate post-translational modifications, expression levels, and protein-protein interactions of thousands of proteins at a time. Complementing the valuable information generated through the integrative knowledge of protein expression and function should enable the development of more efficient diagnostic tools and therapeutic modalities. Here we review redox proteomic studies of some neurodegenerative diseases.

Exogenous application of glucose induces aging in rat cerebral oligodendrocytes as revealed by alteration in telomere length

To investigate aspects of aging on rat oligodendrocytes, cells of an oligodendrocyte cell line, so-called OLN-93, were cultured either in the presence or absence of glucose. Our data demonstrated that glucose-induced aging in vitro caused an elongation and thickening of cell processes and significantly increased the expression of netrin reflecting a more mature state of oligodendrocyte development. A possible age-inducing effect of glucose is also supported by the decrease of ras protein expression and shortening of telomeres in glucose-treated oligodendrocytes. The present study clearly shows that OLN-93 cells are an exciting and suitable model system for the investigation of age-inducing molecules and the analysis of signaling pathways involved in cerebral aging and degenerations.

The advanced glycation end-product Nɛ-(carboxymethyl)lysine level is elevated in cerebrospinal fluid of patients with amyotrophic lateral sclerosis

Oxidative stress is involved in the aetiopathogenesis of amyotrophic lateral sclerosis (ALS), a fatal degenerative disorder. To test whether oxidative stress in ALS is increased and confined to the central nervous system, we have measured the glycoxidation product N(epsilon)-(carboxymethyl)lysine (CML) in serum and cerebrospinal fluid (CSF) samples by means of a novel enzyme immunoassay. Significant increases of CSF/serum ratio of CML in ALS patients (n = 25) as compared to normal controls (n = 20, p = 0.001) and to Alzheimer disease patients (n = 9, p = 0.029) suggest intrathecal production of this glycoxidation product. Measurement of CML levels may provide a novel diagnostic tool and may supplement current monitoring strategies in interventional trials.

Long-Term Intermittent Hypoxia

Humans with long-standing sleep apnea show mixed responses to serotonergic therapies for obstructive sleep apnea. We hypothesize that long-term intermittent hypoxia may result in oxidative injury to upper airway motoneurons, thereby diminishing serotonergic motoneuronal excitation. Unilateral serotonin and glutamate agonist and antagonist microinjections into the hypoglossal motor nuclei in adult rats exposed to 3 weeks of intermittent hypoxia showed reduced hypoglossal nerve responsiveness (logEC50) for serotonin and N-methyl-D-aspartate. However, long-term intermittent hypoxia did not appear to alter hypoglossal response to alpha-amino-3-hydroxy-methylisoxazole-4-propionic acid injections. There was no reduction in hypoglossal motoneuron soma number or in serotonergic postsynaptic receptor mRNA copy numbers within single-cells; in contrast, there was an increase in isoprostanes in the dorsal medulla. Systemic 4-hydroxyl-2,2,6,6-tetramethylpiperidin-1-oxyl (tempol) throughout exposure to intermittent hypoxia improved the EC50 for serotonin to a larger extent than glutamate and normalized medullary isoprostanes. Protein kinase C activity within the hypoglossal nucleus was increased after long-term intermittent hypoxia. These results suggest that long-term intermittent hypoxia reduces serotonergic and N-methyl-D-aspartate excitatory output of hypoglossal nerves, and that reduced excitatory responsiveness and lipid peroxidation are largely prevented with superoxide dismutase treatment throughout hypoxia/reoxygenation. Similar alterations in neurochemical responsiveness may occur in select persons with obstructive sleep apnea.

Proteomic analysis of brain proteins in the gracile axonal dystrophy (gad) mouse, a syndrome that emanates from dysfunctional ubiquitin carboxyl-terminal hydrolase L-1, reveals oxidation of key proteins

Ubiquitin carboxyl-terminal hydrolase L-1 (UCH L-1) is a crucial enzyme for proteasomal protein degradation that generates free monomeric ubiquitin. Our previous proteomic study identified UCH L-1 as one specific target of protein oxidation in Alzheimer's disease (AD) brain, establishing a link between the effect of oxidative stress on protein and the proteasomal dysfunction in AD. However, it is unclear how protein oxidation affects function, owing to the different responses of proteins to oxidation. Analysis of systems in which the oxidized protein displays lowered or null activity might be an excellent model for investigating the effect of the protein of interest in cellular metabolism and evaluating how the cell responds to the stress caused by oxidation of a specific protein. The gracile axonal dystrophy (gad) mouse is an autosomal recessive spontaneous mutant with a deletion on chromosome 5 within the gene encoding UCH L-1. The mouse displays axonal degeneration of the gracile tract. The aim of this proteomic study on gad mouse brain, with dysfunctional UCH L-1, was to determine differences in brain protein oxidation levels between control and gad samples. The results showed increased protein oxidation in thioredoxin peroxidase (peroxiredoxin), phosphoglycerate mutase, Rab GDP dissociation inhibitor alpha/ATP synthase and neurofilament-L in the gad mouse brain. These findings are discussed with reference to the effect of specific protein oxidation on potential mechanisms of neurodegeneration that pertain to the gad mouse.

In vitro reactive nitrating species toxicity in dissociated spinal motor neurons from NFL (-/-) and hNFL (+/+) transgenic mice

We utilized fetal spinal motor neurons isolated from either NFL (-/-) or hNFL (+/+) transgenic mice to determine whether the loss of the low molecular weight neurofilament protein (NFL) places spinal motor neurons at a greater risk for cell death triggered by reactive nitrating species (RNS). After 21 days in serum-free, antibiotic-free medium, both the NFL (-/-) and hNFL (+/+) motor neurons developed neurofilamentous aggregates. Cultures were then exposed to nitric oxide(100 microM NOC 5, 100 microM NOC 12, or 2 mM sodium nitroprusside) or to peroxynitrite (250 mM SIN-1) forvarying intervals. NFL (-/-) cultures demonstrated extensive numbers of apoptotic neurons within six hours and complete cell loss by 24 hours in response to NOC 5 and NOC 12. In contrast, apoptosis was only observed in the motor neurons derived from control (C57bl/6) or hNLF (+/+) mice at 24 hours. In response to 2 mM sodium nitroprusside, necrosis was induced in all cells within 60 minutes. In response to 250 mM SIN-1, both C57bl/6 and hNFL (+/+) cells survived to six hours with only minimal evidence of degeneration while NFL (-/-) motor neurons were necrotic by 60 minutes. These observations suggest that NFL deficient motor neurons are at an enhanced risk of cell death mediated by RNS.

The basic aspects of therapeutics in amyotrophic lateral sclerosis

Once thought to be a single pathological disease state, amyotrophic lateral sclerosis (ALS) is now recognized to be the limited phenotypic expression of a complex, heterogeneous group of biological processes, resulting in an unrelenting loss of motor neurons. On average, individuals affected with the disease live <5 years. In this article, the complex nature of the pathogenesis of ALS, including features of age dependency, environmental associations, and genetics, is reviewed. Once held to be uncommon, it is now clear that ALS is associated with a frontotemporal dementia and that this process may reflect disturbances in the microtubule-associated tau protein metabolism. The motor neuron ultimately succumbs in a state where significant disruptions in neurofilament metabolism, mitochondrial function, and management of oxidative stress exist. The microenvironment of the neuron becomes a complex milieu in which high levels of glutamate provide a source of chronic excitatory neurotoxicity, and the contributions of activated microglial cells lead to further cascades of motor neuron death, perhaps serving to propagate the disease once established. The final process of motor neuron death encompasses many features of apoptosis, but it is clear that this alone cannot account for all features of motor neuron loss and that aspects of a necrosis-apoptosis continuum are at play. Designing pharmacological strategies to mitigate against this process thus becomes an increasingly complex issue, which is reviewed in this article.

Neurotoxicity of acetaldehyde-derived advanced glycation end products for cultured cortical neurons

The Maillard reaction that leads to the formation of advanced glycation end products (AGEs) plays an important role in the pathogenesis of angiopathy in diabetic patients, in aging, and in neurodegenerative processes. We hypothesize that acetaldehyde (AA), one of the main metabolites of alcohol, may be involved in alcohol-induced neurotoxicity in vivo by formation of AA-derived AGEs (AA-AGEs) with brain proteins. Incubation of cortical neurons with AA-AGE produced a dose-dependent increase in neuronal cell-death, and the neurotoxicity of AA-AGE was neutralized by the addition of an anti-AA-AGE-specific antibody, but not by anti-N-ethyllysine (NEL) antibody. The AA-AGE epitope was detected in human brain of alcoholism. We propose that the structural epitope AA-AGE is an important toxic moiety for neuronal cells in alcoholism.

Pathways to motor neuron degeneration in transgenic mouse models

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurological disorder characterized by the selective loss of motor neurons. A pathological hallmark of both sporadic and familial ALS is the presence of abnormal accumulations of neurofilament and peripherin proteins in motor neurons. In the past decade, transgenic mouse approaches have been used to address the role of such cytoskeletal abnormalities in motor neuron disease and also to unravel the pathogenesis caused by mutations in the gene coding for superoxide dismutase 1 (SOD1) that account for ~20% of familial ALS cases. In mouse models, disparate effects could result from different types of intermediate filament (IF) aggregates. Perikaryal IF accumulations induced by the overexpression of any of the three wild-type neurofilament proteins were quite well tolerated by motor neurons. Indeed, perikaryal swellings provoked by NF-H overexpression can even confer protection against toxicity of mutant SOD1. Other types of IF aggregates seem neurotoxic, such as those found in transgenic mice overexpressing either peripherin or an assembly-disrupting NF-L mutant. Moreover, understanding the toxicity of SOD1 mutations has been surprisingly difficult. The analysis of transgenic mice expressing mutant SOD1 has yielded complex results, suggesting that multiple pathways may contribute to disease that include the involvement of non-neuronal cells.

Protein glycation: creation of catalytic sites for free radical generation

In a glycation reaction, alpha-dicarbonyl compounds such as deoxyglucosone, methylglyoxal, and glyoxal are more reactive than the parent sugars with respect to their ability to react with amino groups of proteins to form inter- and intramolecular cross-links of proteins, stable end products called advanced Maillard products or advanced end products (AGEs). The AGEs, which are irreversibly formed, accumulate with aging, atherosclerosis, and diabetes mellitus, and are especially associated with long-lived proteins such as collagens, lens crystallins, and nerve proteins. It was suggested that the formation of AGEs not only modifies protein properites but also induces biological damage in vivo. In this report, we summerize results obtained from our studies for (1) identifying the structure of the cross-linked radical species formed in the model system-the reaction between alpha-dicarbonyl methylglyoxal with amino acids, and (2) the reactivity of the radical center of the protein created by the similar reaction. These results indicate that glycation of protein generates active centers for catalyzing one-electron oxidation-reduction reactions. This active center, which exhibits enzyme-like character, is suggested to be the cross-linked Schiff-based radical cation of the protein. It mimics the characteristics of the metal-catalyzed oxidation system. These results together indicate that glycated proteins accumulated in vivo provide stable active sites for catalyzing the formation of free redicals.

Neurofilament homeostasis and motoneurone degeneration

Neurofilament disorganisation is a hallmark of various neurodegenerative diseases. We review here current knowledge of neurofilament structure, gene expression and function. Neurofilament involvement in motoneurone neurological diseases is discussed in view of recent data from transgenic and spontaneous mouse mutants. In the mammalian neurone, the three neurofilament subunits are assembled into intermediate filaments as obligate heteropolymers. The subunits are expressed differentially during development and adult life according to the cell type and its physiological state. In addition to the well-established role of neurofilaments in the control of axonal calibre, there is increasing evidence that neurofilaments can interact with other cytoskeletal components and can modulate the axoplasmic flow. Although the extent to which neurofilament abnormalities contribute to the pathogenesis in human diseases remains unknown, emerging evidence suggests that disorganised neurofilaments can provoke degeneration and death of neurones. BioEssays 23:24-33, 2001.

Progress in the pathogenesis of amyotrophic lateral sclerosis

This decade has seen the discovery of one cause for amyotrophic lateral sclerosis (ALS)--mutations in the copper/zinc superoxide dismutase (SOD1) gene. Mutant SOD1 has provided an invaluable tool for transgenic and cellular experiments designed to elicit the biochemical pathways that are disturbed in ALS. We highlight recent advances in ALS research, including diagnostic issues, new loci for ALS genes, and progress in understanding the toxicity of mutant SOD1. The evidence for persistant viral infection, glutamate-mediated excitotoxicity, oxidative stress, altered neurofilament and peripherin expression, disrupted axonal transport, neurotrophin deficiency, and mitochondrial dysfunction are critically reviewed. As yet, no consensus has been achieved on the pathways that lead to selective neuronal death, and the underlying causes are still unknown in the vast majority of patients. Further clues about genetic susceptibility and environmental triggers are urgently needed so that more effective treatments for ALS can be developed, with the ultimate goal being prevention.

Cytoskeletal abnormalities in amyotrophic lateral sclerosis: beneficial or detrimental effects?

Cytoskeletal abnormalities have been reported in cases of amyotrophic lateral sclerosis (ALS) including abnormal inclusions containing neurofilaments (NFs) and/or peripherin, reduced mRNA levels for the NF light (NF-L) protein and mutations in the NF heavy (NF-H) gene. Recently, transgenic mouse approaches have been used to address whether cytoskeletal changes may contribute to motor neuron disease. Mice lacking one of the three NF subunits are viable and do not develop motor neuron disease. Nonetheless, mice with null mutations for NF-L or for both NF-M and NF-H genes developed severe atrophy of ventral and dorsal root axons. The atrophic process is associated with hind limb paralysis during aging in mice deficient for both NF-M and NF-H proteins. The overexpression in mice of transgenes coding for wild-type or mutant NF proteins can provoke abnormal NF accumulations, axonal atrophy and sometimes motor dysfunction. However, the perikaryal NF accumulations are generally well tolerated by motor neurons and, except for expression of a mutant NF-L transgene, they did not provoke massive motor neuron death. Increasing the levels of perikaryal NF proteins may even confer protection in motor neuron disease caused by ALS-linked mutations in the superoxide dismutase (SOD1). In contrast, the overexpression of wild-type peripherin, a type of IF gene upregulated by inflammatory cytokines, provoked the formation of toxic IF inclusions with the high-molecular-weight NF proteins resulting in the death of motor neurons during aging. These results together with the detection of peripherin inclusions at early stage of disease in mice expressing mutant SOD1 suggest that IF inclusions containing peripherin may play a contributory role in ALS pathogenesis.

Immunohistochemistry of advanced glycation end products in neurofilamentous axonal spheroids induced by beta-beta'-iminodipropionitrile in lower motor neurons of rat

Chronic parenteral administration of beta-beta'-iminodipropionitrile (IDPN) in adult female rats induces large neurofilament-rich axonal spheroids (AXS) in spinal motor neurons closely resembling those AXS in early phases of amyotrophic lateral sclerosis. Immunohistochemistry of advanced glycosylation end-products (AGEs) in axonal spheroids was performed in the present study. Anti-AGE and anti-neurofilament antibodies strongly co-labeled IDPN-induced axonal spheroids, whereas motor neuron soma showed little AGE immunoreactivity. In an attempt to modify and intensify glycosylation, another group of IDPN rats was made hyperglycemic with streptozotocin after IDPN intoxication. These hyperglycemic rats showed AXS with striking AGE immunoreactivity. An additional group of rats made hyperglycemic before IDPN intoxication showed markedly diminished AXS formation, with a few small AGE-positive AXS in anterior horns. Findings suggest that AGEs are involved in neurofilament crosslinking as well as disassembly of neurofilament induced by IDPN with or without hyperglycemia. Hyperglycemia did not intensify neurofilament aggregation. Additional immunohistochemistry revealed not only aberrant phosphorylation, but also intense local production of Cu/Zn superoxide dismutase and nitrotyrosine in axonal spheroids, probably secondary to superoxide generation as a consequence of AGE production at neurofilament protein, impeding its assembly as hypothesized in motoneuron diseases.

Recent advances in amyotrophic lateral sclerosis

The mechanisms by which mutations of the SOD1 gene cause selective motor neuron death remain uncertain, although interest continues to focus on the role of peroxynitrite, altered peroxidase activity of mutant SOD1, changes in intracellular copper homeostasis, protein aggregation, and changes in the function of glutamate transporters leading to excitotoxicity. Neurofilaments and peripherin appear to play some part in motor neuron degeneration, and amyotrophic lateral sclerosis is occasionally associated with mutations of the neurofilament heavy chain gene. Linkage to several chromosomal loci has been established for other forms of familial amyotrophic lateral sclerosis, but no new genes have been identified. In the clinical field, interest has been shown in the population incidence and prevalence of amyotrophic lateral sclerosis and the clinical variants that cause diagnostic confusion. Transcranial magnetic stimulation has been used to detect upper motor neuron damage and to explore cortical excitability in amyotrophic lateral sclerosis, and magnetic resonance imaging including proton magnetic resonance spectroscopy and diffusion weighted imaging also provide useful information on the upper motor neuron lesion. Aspects of care including assisted ventilation, nutrition, and patient autonomy are addressed, and underlying these themes is the requirement to measure quality of life with a new disease-specific instrument. Progress has been made in developing practice parameters. Riluzole remains the only drug to slow disease progression, although interventions such as non-invasive ventilation and gastrostomy also extend survival.

Enhanced free radical generation of FALS-associated Cu,Zn-SOD mutants

Familial amyotrophic lateral sclerosis (FALS) is an inherited disorder of motor neurons, which is associated with missense mutations in the Cu,Zn-superoxide dismutase (Cu,Zn-SOD) gene. Mice from the G93A transgenic line were reported to develop a syndrome of FALS. The fact that the symptoms occurred against a background of normal mouse Cu,Zn-SOD activity suggests that dominant, gain-of-function mutations in SOD play a role in the pathogenesis of FALS. We investigated the nature of this gain-of-function of FALS mutants. We have previously reported that Cu,Zn-SOD has the free radical-generating function in addition to normal dismutation activity. These two enzymic activities were compared by using mutants (G93A and A4V) and the wild-type Cu,Zn-SOD prepared by recombinant method. Our results showed that the wild-type, G93A, and A4V enzymes have identical dismutation activity. However, the free radical-generating function of the G93A and A4V mutants, as measured by the spin trapping and EPR method, is enhanced relative to that of the wild-type enzyme (wild type < G93A < A4V), particularly at lower H(2)O(2) concentrations. This is due to the decrease in the K(m) value for H(2)O(2), wild-type > G93A > A4V. The catalytic activity to generate free radicals is correlated to the clinical severity of the disorder induced by these mutant enzymes. Furthermore, we found that intact FALS mutants failed to enhance tyrosine nitration. Together our results indicate that the amyotrophic lateral sclerosis symptoms are not caused by the reduction of Cu,Zn-SOD dismutation activity with the mutant enzymes; rather, it is induced in part by enhancement of the free radical-generating function.

Neurofilament metabolism in sporadic amyotrophic lateral sclerosis

Although the role of intraneuronal neurofilamentous aggregates in the pathogenesis of ALS is unknown, their presence forms a key neuropathological hallmark of the disease process. Conversely, the experimental induction of neurofilamentous aggregates in either neurotoxic or transgenic mice gives rise to motor system degeneration. To determine whether alterations in the physiochemical properties of NF are present in sporadic ALS, we purified NF subunit proteins from cervical spinal cord of ALS and age-matched control patients. The cytoskeleton-enriched, Triton X-100 insoluble fraction was further separated into individual NF subunits using hydroxyapatite HPLC. We observed no differences between control and ALS in the characteristics of NFH, including migration patterns on 2D-IEF, sensitivity to E. coli, alkaline phosphatase mediated dephosphorylation, peptide mapping, or proteolysis (calpain, calpain/calmodulin mediated, phosphorylated or dephosphorylated NFH). NFL showed no differences in 2D-IEF migration patterns, peptide mapping, or the extent of NFL nitrotyrosine immunoreactivity in either the Triton soluble or insoluble fractions. The latter observation demonstrated that NFL nitration is a ubiquitous occurrence in neurons and suggests that NFL might function as a sink for free reactive nitrating species. In contrast to the lack of differences in the post-translational processing of NF in ALS, we did observe a selective suppression of NFL steady state mRNA levels in the limb innervating lateral motor neuron column of ALS. This occurred in the absence of modifications in NFH, NFM or neuronal nitric oxide synthase (Type I NOS; nNOS) steady state mRNA levels. Coupled with previous observations of nNOS immunoreactivity co-localizing with NF aggregates in ALS motor neurons, this suggests activation of the nNOS enzyme complex in ALS, which would be predicted to contribute directly to the generation of reactive nitrating species. Given this, the isolated suppression of NFL steady state mRNA levels in ALS may indicate that ALS motor neurons are at an intrinsic deficit in the ability to buffer free reactive nitrating species.

A receptor for advanced glycosylation endproducts (AGEs) is colocalized with neurofilament-bound AGEs and SOD1 in motoneurons of ALS: immunohistochemical study

Neurofilament (NF)-bound AGEs colocalize immunochemically with SOD1 in the motoneurons of patients with ALS. Among three types of AGE receptors reported in the human brain, AGE-R1 (oligosaccharyltransferase family) and AGE-R2 (substrate of protein kinase C) have been found in neurons, while AGE-R3 is restricted to glia. The present study investigates which of these receptors may be responsible for binding AGEs in the NF conglomerates of motoneurons. Immunostaining of paraffin sections from eight ALS patients (five sporadic and three familial) and three control cases was performed with antibodies directed against R1 and R2, in parallel with those against AGEs and SOD1. The sites of AGE-R1 immunoreactivity (IR) in motoneurons were in conformity to those of NF-associated AGE and SOD1 IRs. By contrast, the IR of R2 was negative in NF conglomerates. Negative R2 IR for NF conglomerates was outlined by surrounding coarse R2 immunopositive granules in the perikaryon. No IR for R1 or R2 was found in hyaline or Bunina inclusions. There was no extraneuronal expression of IR for AGE-R1 or AGEs in microglia or astroglia around the NF accumulation. The colocalization of AGE, AGE-R1, and SOD1 at NF conglomerates in motoneurons supports the notion that AGE-mediated oxidative stress and protein aggregation may be implicated in NF conglomeration and ALS pathogenesis.

Pathogenesis of amyotrophic lateral sclerosis: a critical review

Amyotrophic lateral sclerosis is a neurodegenerative disease with unknown pathogenesis. It is a relatively common disorder of adults (2-4 per 100,000 incidence) and leads to death from respiratory failure. There is no cure at this time, and available treatment and management can at best extend survival to a modest degree. Increasing our understanding of the pathogenesis of this disease is essential to the development of more effective treatments. The level of research interest is very high, and yearly reviews of the literature are helpful in assessing progress.

Neurofilament functions in health and disease

Transgenic approaches have recently been used to investigate the functions of neuronal intermediate filaments. Gene knockout studies have demonstrated that neurofilaments are not required for axogenesis and that individual neurofilament proteins play distinct roles in filament assembly and in the radial growth of axons. The involvement of neurofilaments in disease is supported by the discovery of novel mutations in the neurofilament heavy gene from cases of amyotrophic lateral sclerosis and by reports of neuronal death in mouse models expressing neurofilament and alpha-internexin transgenes. However, mouse studies have shown that axonal neurofilaments are not required for pathogenesis caused by mutations in superoxide dismutase and that increasing perikaryal levels of neurofilament proteins may even confer protection in this disease.

Neurotoxicity of methylglyoxal and 3-deoxyglucosone on cultured cortical neurons: synergism between glycation and oxidative stress, possibly involved in neurodegenerative diseases

In this study, we investigate the neurotoxicity of glycation, particularly early-stage glycation, and its mechanisms, which are possibly synergized with oxidative stress. Methylglyoxal (MG) and 3-deoxyglucosone (3DG), intermediate products of glycation, are known to further accelerate glycation and advanced glycation endproducts (AGEs) formation. Both compounds showed neurotoxicity on cultured cortical neurons and these effects were associated with reactive oxygen species production followed by neuronal apoptosis. Pretreatment with N-acetylcysteine induced neuroprotection against MG and 3DG. Cotreatment, but not pretreatment, with aminoguanidine protected neurons against the neurotoxicities of both compounds. The present study provides the first evidence that MG and 3DG are neurotoxic to cortical neurons in culture. Interference with the process by which glycation and AGEs formation occur may provide new therapeutic opportunities to reduce the pathophysiological changes associated with neurodegeneration, if, as indicated here, the participation of glycoxidation in the pathogenesis of neurodegenerative diseases is essential.